chore(backport release-1.8): docs: add v1.8.0 release notes (#5269)

Author: akuitybot

docs/docs/80-release-notes/91-v1.8.0.md

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+🚀 The Kargo team is proud to unveil our feature-packed v1.8.0 release!
+
+## ⚠️ Breaking Changes
+
+The format of logs emitted by Kargo components has changed slightly.
+
+## ⚠️ New Deprecations
+
+None
+
+## ✨ Noteworthy Features
+
+Now the fun stuff! As usual, we packed so much great stuff into this release that we'd be here a very long time if we were to cover all of it in detail. Here's our still longer-than-usual list of new or improved features that we regard as being especially noteworthy.
+
+* **`Freight` creation criteria:** `Warehouse` resources can now use expression-based criteria to control when automatic `Freight` creation occurs. This solves the long-standing problem of `Warehouse`s creating `Freight` with incompatible artifact combinations when subscribed to multiple repositories.
+
+  With a `Warehouse`'s `Freight` creation policy set to `Automatic`, you can now provide criteria as an expression that must evaluate to `true` for automatic `Freight` creation to proceed. For example, to ensure `Freight` is created only when front end and back end container images have matching version tags:
+
+  ```expr
+  imageFrom('example/front-end').Tag == imageFrom('example/back-end').Tag
+  ```
+
+  You can read more about this new feature in the [Working with Warehouses](https://docs.kargo.io/user-guide/how-to-guides/working-with-warehouses#automatic-freight-creation) section of Kargo's documentation.
+  
+* **Syncing to an upstream `Stage`**: A new auto-promotion policy, `MatchUpstream`, allows `Stage` resource to perpetually sync with their immediate upstream `Stage` instead of always promoting the newest available `Freight`. This is ideal for scenarios like keeping a performance testing environment synced with the exact same artifacts currently being tested in a QA environment.
+
+  You can read more about this feature in the [Working with Stages](https://docs.kargo.io/user-guide/how-to-guides/working-with-stages#auto-promotion) section of Kargo's documentation.
+
+* **`git-merge-pr` promotion step**: A new promotion step enables automated merging of pull requests. This addresses requests from users who want to open PRs only for the audit purposes, then merge them immediately. **This feature is in beta state.**
+
+  You can read more about this feature on the `git-merge-pr` promotion step's [reference page](https://docs.kargo.io/user-guide/reference-docs/promotion-steps/git-merge-pr).
+
+* **New and improved metadata support**: You can now propagate important context between `Stage`s using a new `set-metadata` promotion step. Arbitrary metadata attached to `Freight` and `Stage` resources can be retrieved using new `stageMetadata()` and `freightMetadata()` expression functions. This enables use cases like associating a Slack thread ID with a `Freight` resource and sending an update to that thread each time the `Freight` is promoted to a different `Stage`.
+
+  To learn more about these features, refer to the reference docs for the [`set-metadata`](https://docs.kargo.io/user-guide/reference-docs/promotion-steps/set-metadata) promotion step as well as the [`freightMetadata()`](https://docs.kargo.io/user-guide/reference-docs/expressions#freightmetadatafreightname) and [`stageMetadata()`](https://docs.kargo.io/user-guide/reference-docs/expressions#stagemetadatastagename) sections of the expressions reference docs.
+
+* **Improved OIDC claim-to-ServiceAccount mappings:** The system for mapping authenticated users to Kubernetes `ServiceAccount`s has been overhauled with a new format that supports special characters not permitted in Kubernetes annotation keys. The change is largely transparent - existing mappings will migrate automatically with no user action required.
+
+  You can read more about mappings in the [operator guide](https://docs.kargo.io/operator-guide/security/access-controls#user-to-serviceaccount-mappings) and [user guide](https://docs.kargo.io/user-guide/security/access-controls/#user-to-serviceaccount-mappings).
+
+* **Harbor webhook receiver:** A new webhook receiver triggers `Warehouse` artifact discovery when container images or Helm charts are pushed to [Harbor](https://goharbor.io/) registries.
+
+  To learn more, refer to the [Harbor webhook receiver](https://docs.kargo.io/user-guide/reference-docs/webhook-receivers/harbor/) reference docs. Special thanks to @ahockersten for this contribution.
+
+* **Logging improvements**: We've replaced Kargo's internal logging framework, resulting in minor format changes to unstructured logs and new support for structured JSON logs (opt-in via chart settings).
+
+* **Favorite `Project`s:** `Project`s can now be "starred" for quick access - perfect for organizations with a very large number of `Project`s.
+
+* **Drag 'n' drop `Promotion`s:** Need we say more?
+
+* **New `Freight` assembly option:** A new `Freight` "clone" feature lets you use existing `Freight` as a template, selecting only the artifact revisions you want to change from the original.
+
+## 🙏 Special Thanks
+
+Thank you, as always, to community members who made their first contribution to Kargo in this release!
+
+* @mikedougherty
+* @ahockersten
+* @gladavius
+* @ianstanton
+* @kyounghunJang
+* @jobama7860
+
+**Full Changelog**: https://github.com/akuity/kargo/compare/v1.7.5...v1.8.0