FeatureToggle: Disable dashgpt by default and mark it as preview

[ivanortegaalba]

DashGPT features were announced in 10.2.0 as a public preview. However, we marked them as GA in the 10.2.1 by mistake.

We discovered there is a performance issue associated with this feature flag being enabled by default. Also, to be congruent with the 10.2 minor, we should mark it back as a public preview.

[grafana-delivery-bot]

The backport to v10.2.x failed:

The process '/usr/bin/git' failed with exit code 1

To backport manually, run these commands in your terminal:

# Fetch latest updates from GitHub
git fetch
# Create a new branch
git switch --create backport-78348-to-v10.2.x origin/v10.2.x
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x ddfe4e1bddabcaeab759e2ea9a6d590db2ff021b

When the conflicts are resolved, stage and commit the changes:

git add . && git cherry-pick --continue

If you have the GitHub CLI installed:

# Push the branch to GitHub:
git push --set-upstream origin backport-78348-to-v10.2.x
# Create the PR body template
PR_BODY=$(gh pr view 78348 --json body --template 'Backport ddfe4e1bddabcaeab759e2ea9a6d590db2ff021b from #78348{{ "\n\n---\n\n" }}{{ index . "body" }}')
# Create the PR on GitHub
echo "${PR_BODY}" | gh pr create --title "[v10.2.x] FeatureToggle: Disable `dashgpt` by default and mark it as preview" --body-file - --label "type/bug" --label "type/docs" --label "area/backend" --label "add to changelog" --label "backport" --base v10.2.x --milestone 10.2.x --web

Or, if you don't have the GitHub CLI installed (we recommend you install it!):

# Push the branch to GitHub:
git push --set-upstream origin backport-78348-to-v10.2.x

# Create a pull request where the `base` branch is `v10.2.x` and the `compare`/`head` branch is `backport-78348-to-v10.2.x`.

# Remove the local backport branch
git switch main
git branch -D backport-78348-to-v10.2.x