feat: support application settings

[BoxBoxJason]

Description of your changes

The goal of this PR is to introduce a way to support application settings configuration for the gitlab instance using the provider. This is greatly inspired from the terraform gitlab provider application settings resource

Fixes #243

I have:

• Read and followed Crossplane's contribution process.
• Run make reviewable test to ensure this PR is ready for review.

What was added:

• A new "instance" api, in addition to the projects and groups, to update instance wide settings (for self hosted instances), it does not work on gitlab.com of course.
• A new "ApplicationSettings" CRD / controller / api to reconcile gitlab instance settings
• two generation function that are used to make type assignments / comparisons / generations from reflection of gitlab client-go types

How has this code been tested

• I have a self hosted gitlab instance in my homelab (I can share the link with reviewers if required)

• I don't use docker (and I don't have it installed), instead I use podman on my Fedora 43 (Workstation) machine

• I setup a kind cluster with the KIND_EXPERIMENTAL_PROVIDER=podman, using kind create cluster --name gitlab

• I install the crossplane helm chart

  1. helm repo add crossplane-stable https://charts.crossplane.io/stable
  2. helm install crossplane --namespace crossplane-system --create-namespace crossplane-stable/crossplane

• I build the go code make go.build and then run it ./_output/bin/linux_amd64/provider --debug

• I create the secret with my PAT (admin permissions) k create secret generic gitlab-credentials -n crossplane-system --from-literal=token=EXAMPLE_VALUE

• I apply the providerconfig manifest:

  apiVersion: gitlab.m.crossplane.io/v1beta1
  kind: ProviderConfig
  metadata:
    name: gitlab-provider
    namespace: default
  spec:
    baseURL: https://REDACTED_URL/
    credentials:
      source: Secret
      method: PersonalAccessToken
      secretRef:
        namespace: crossplane-system
        name: gitlab-credentials
        key: token

• I apply the applicationSettings manifest (this is a reduced number of values to not jam the description):

  apiVersion: instance.gitlab.m.crossplane.io/v1alpha1
  kind: ApplicationSettings
  metadata:
    name: boxboxjason-settings
    namespace: default
  spec:
    providerConfigRef:
      name: gitlab-provider
      kind: ProviderConfig
    forProvider:
      maxArtifactsSize: 222
      silentModeEnabled: true

• I check that parameters are applied and no errors appears.

• I update the CRD with new values and check again for errors / that they are applied

• I update the gitlab settings manually and confirm that they are reconciled

• I delete the resource and check that nothing new happens, the resource gets deleted properly