docs: Update variable formatting

[JStickler]

What this PR does / why we need it:

Updates replacement variables to match proper formatting (upper case, underscores).

[github-actions]

💻 Deploy preview deleted (docs: Update variable formatting).

[loki-gh-app]

The backport to release-3.4.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-19610-to-release-3.4.x origin/release-3.4.x
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x 34f5ae3cd875ab599e93e657ccfbfb5f7cdcb22e

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-19610-to-release-3.4.x
# Create the PR body template
PR_BODY=$(gh pr view 19610 --json body --template 'Backport 34f5ae3cd875ab599e93e657ccfbfb5f7cdcb22e from #19610{{ "\n\n---\n\n" }}{{ index . "body" }}')
# Create the PR on GitHub
echo "${PR_BODY}" | gh pr create --title 'docs: Update variable formatting (backport release-3.4.x)' --body-file - --label 'size/M' --label 'type/docs' --label 'backport' --base release-3.4.x --milestone release-3.4.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-19610-to-release-3.4.x

# Create a pull request where the `base` branch is `release-3.4.x` and the `compare`/`head` branch is `backport-19610-to-release-3.4.x`.

# Remove the local backport branch
git switch main
git branch -D backport-19610-to-release-3.4.x

[loki-gh-app]

The backport to release-3.5.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-19610-to-release-3.5.x origin/release-3.5.x
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x 34f5ae3cd875ab599e93e657ccfbfb5f7cdcb22e

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-19610-to-release-3.5.x
# Create the PR body template
PR_BODY=$(gh pr view 19610 --json body --template 'Backport 34f5ae3cd875ab599e93e657ccfbfb5f7cdcb22e from #19610{{ "\n\n---\n\n" }}{{ index . "body" }}')
# Create the PR on GitHub
echo "${PR_BODY}" | gh pr create --title 'docs: Update variable formatting (backport release-3.5.x)' --body-file - --label 'size/M' --label 'type/docs' --label 'backport' --base release-3.5.x --milestone release-3.5.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-19610-to-release-3.5.x

# Create a pull request where the `base` branch is `release-3.5.x` and the `compare`/`head` branch is `backport-19610-to-release-3.5.x`.

# Remove the local backport branch
git switch main
git branch -D backport-19610-to-release-3.5.x