fix(release): remove changelog.disable to allow --release-notes to work (#2705)

## Summary

- Remove `changelog.disable: true` from `.goreleaser.yml` because it
suppresses `--release-notes` content, resulting in empty draft release
bodies.

`changelog.disable: true` skips the entire changelog pipe
([source](https://github.com/goreleaser/goreleaser/blob/main/internal/pipe/changelog/changelog.go#L45-L51)),
which means `--release-notes` file loading never executes. Without
`disable`, `--release-notes` still skips GoReleaser's own changelog
generation via an early return
([source](https://github.com/goreleaser/goreleaser/blob/main/internal/pipe/changelog/changelog.go#L73-L74)),
so only the git-cliff content is used.

Author: Duologic

.goreleaser.yml

@@ -74,5 +74,4 @@ signs:
 release:
   # If you want to manually examine the release before it's live, uncomment this line:
   draft: true
-changelog:
-  disable: true
+

README.md

@@ -142,4 +142,4 @@ Currently there are a few manual steps to this:
 
    The Action creates the release, but leaves it in "draft" state. Open it up in
    a [browser](https://github.com/grafana/terraform-provider-grafana/releases)
-   and if all looks well, click the `Auto-generate release notes` button and mash the publish button.
+   and if all looks well, publish the release. Release notes are generated automatically by git-cliff.