Explore: Avoid reinitializing graph on every query run

[Elfo404]

What is this feature?

Fixes the structureRev logic in explore so that the first result is not 0, which would cause the graph to re-init at every render.

Why do we need this feature?

1 - improves performance as no initialization is done if not needed
2 - having it to 0 would cause the graph to re-init at every render, due to some timing issues with changing queries and zooming, thous would break explore. see #77237 for details

Who is this feature for?

Explore users

Which issue(s) does this PR fix?:

Fixes #77237

Special notes for your reviewer:

Please check that:

• It works as expected from a user's perspective.
• If this is a pre-GA feature, it is behind a feature toggle.
• The docs are updated, and if this is a notable improvement, it's added to our What's New doc.

[gtk-grafana]

Nothing like a single char PR! Works good for me locally, thanks for finding the fix for this so quickly!

[github-actions]

Backend code coverage report for PR #77281
No changes

[github-actions]

Frontend code coverage report for PR #77281

Plugin	Main	PR	Difference
explore	85.33%	85.33%	0%

[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-77281-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 bf554d121cc116457f3432f2448314381b234016

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-77281-to-v10.2.x
# Create the PR body template
PR_BODY=$(gh pr view 77281 --json body --template 'Backport bf554d121cc116457f3432f2448314381b234016 from #77281{{ "\n\n---\n\n" }}{{ index . "body" }}')
# Create the PR on GitHub
echo "${PR_BODY}" | gh pr create --title "[v10.2.x] Explore: Avoid reinitializing graph on every query run" --body-file - --label "type/bug" --label "area/explore" --label "area/frontend" --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-77281-to-v10.2.x

# Create a pull request where the `base` branch is `v10.2.x` and the `compare`/`head` branch is `backport-77281-to-v10.2.x`.

# Remove the local backport branch
git switch main
git branch -D backport-77281-to-v10.2.x