Fix datadog-service does not show up in under `Observability` or `SLI Providers` on Keptn integrations page

[vadasambar]

Problem statement.
This is a problem with the post 0.15.0 version of datadog-service. Originally noticed by @StackScribe on slack.

datadog-service doesn't show up under Observability or SLI Providers section

This happens because the some versions of datadog-service do not have the right keywords
https://github.com/keptn-sandbox/artifacthub/blob/9cd650443500d0c3c9dfa81bf43ac5c34a798740/datadog-service/0.19.0/artifacthub-pkg.yml#L9-L11
As opposed to 0.15.0 version:
https://github.com/keptn-sandbox/artifacthub/blob/d4d94067d033ca1627ca4f7880eb1918cd13daee/datadog-service/0.15.0/artifacthub-pkg.yml#L9-L14

Describe the solution you'd like
We need to add the following keywords to artifacthub-pkg.yml of all datadog-service folders listed here (if the keyword is already there skip it):

- keptn
- sandbox
- observability
- monitoring
- sli-provider
- datadog
- datadog-service

TODO

• Raise a PR with the above change
• Ask for review in #keptn-integrations channel (mention @vadasambar so that he can help you out in case of problems)
• Get the PR reviewed (note: you probably won't have the permission to merge the PR in https://github.com/keptn-contrib/artifacthub repo. Ask the reviewer to merge the PR)
• DONE

[tarangverma]

can i work on this issue...

[vadasambar]

I have assigned you to the issue. Thank you!