Add remaining [plugin] fields to Grafanas.spec.config.plugins

[meln5674]

Description

Added the following fields to Grafana.spec.config.plugins

• allow_loading_unsigned_plugins
• plugin_admin_enabled
• plugin_catalog_url
• plugin_catalog_hidden_plugins
• (plugin_admin_external_manage_enabled deliberately omitted as it only applied to Grafana Cloud)

Added CRD field docstrings copied from official grafana documentation.

Added example manifest demonstrating usage

Relevant issues/tickets

Fixes #801

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist

• This change requires a documentation update
• I have added tests that prove my fix is effective or that my feature works
• I have added a test case that will be used to verify my changes
• Verified independently on a cluster by reviewer

Verification steps

kubectl apply -f deploy/examples/GrafanaDevEnv.yaml
kubectl get -o yaml configmap grafana-config

[NissesSenap]

LGTM, great that you added good comments as well.