docs: fix deployment mode in Helm example

[JStickler]

What this PR does / why we need it:

Fixes issue reported via docs @ grafana email.

This update was already made in main as part of #12641 but needs to be published to 3.0.

[paul1r]

deploymentMode

[grafanabot]

The backport to release-3.0.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-13025-to-release-3.0.x origin/release-3.0.x
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x 876d9bae21088568a1e4018e15aec23377f0912d

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-13025-to-release-3.0.x
# Create the PR body template
PR_BODY=$(gh pr view 13025 --json body --template 'Backport 876d9bae21088568a1e4018e15aec23377f0912d from #13025{{ "\n\n---\n\n" }}{{ index . "body" }}')
# Create the PR on GitHub
echo "${PR_BODY}" | gh pr create --title 'chore: [release-3.0.x] docs: fix deployment mode in Helm example' --body-file - --label 'size/XS' --label 'type/docs' --label 'backport' --base release-3.0.x --milestone release-3.0.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-13025-to-release-3.0.x

# Create a pull request where the `base` branch is `release-3.0.x` and the `compare`/`head` branch is `backport-13025-to-release-3.0.x`.

# Remove the local backport branch
git switch main
git branch -D backport-13025-to-release-3.0.x