[DOC] Remove --stability-level for Alloy v1.2

[knylander-grafana]

Changes the command line for starting Alloy to not use --stability-level when starting Alloy v1.2.

This PR should go live when Alloy 1.2 is released.

[github-actions]

This PR must be merged before a backport PR will be created.

[github-actions]

This PR must be merged before a backport PR will be created.

[clayton-cornell]

Looks OK to me. Everything lines up :-)

[korniltsev]

lgtm, thanks \m/

[clayton-cornell]

Line 12-14 in docs/sources/configure-client/grafana-agent/java/_index.md should probably be updated as well. River only applies to Agent Flow. Alloy uses https://grafana.com/docs/alloy/latest/concepts/configuration-syntax/ (which is the same as River, but it's not called River in Alloy.

[knylander-grafana]

Line 12-14 in docs/sources/configure-client/grafana-agent/java/_index.md should probably be updated as well. River only applies to Agent Flow. Alloy uses grafana.com/docs/alloy/latest/concepts/configuration-syntax (which is the same as River, but it's not called River in Alloy.

I've updated the text and links. Let me know if what I added is correct.

[github-actions]

The backport to release/v1.6 failed:

Validation Failed: "Could not resolve to a node with the global id of 'T_kwDOAG3Mbc4AczmP'."

To backport manually, run these commands in your terminal:

# Fetch latest updates from GitHub
git fetch
# Create a new branch
git switch --create backport-3382-to-release/v1.6 origin/release/v1.6
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x dfd129c09f3020d65193d849194fc0b3cabb58a2

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-3382-to-release/v1.6
# Create the PR body template
PR_BODY=$(gh pr view 3382 --json body --template 'Backport dfd129c09f3020d65193d849194fc0b3cabb58a2 from #3382{{ "\n\n---\n\n" }}{{ index . "body" }}')
# Create the PR on GitHub
echo "${PR_BODY}" | gh pr create --title '[release/v1.6] [DOC] Remove --stability-level for Alloy v1.2' --body-file - --label 'type/docs' --label 'backport' --base release/v1.6 --milestone release/v1.6 --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-3382-to-release/v1.6

# Create a pull request where the `base` branch is `release/v1.6` and the `compare`/`head` branch is `backport-3382-to-release/v1.6`.

# Remove the local backport branch
git switch main
git branch -D backport-3382-to-release/v1.6