[OpenAPI] Add securitySchemes and security in overlays

[lcawl]

Relates to elastic/docs-content#192

This PR adds overlays for the missing securityScheme and security objects.

The result is that the Elasticsearch API documents will have a page equivalent to this: https://www.elastic.co/docs/api/doc/serverless/authentication

[kilfoyle]

LGTM! 🌵

[github-actions]

The backport to 8.16 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 working tree
git worktree add .worktrees/backport-8.16 8.16
# Navigate to the new working tree
cd .worktrees/backport-8.16
# Create a new branch
git switch --create backport-3198-to-8.16
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x --mainline 1 0b00127e17e82f919ab246388252131269a4488c
# Push it to GitHub
git push --set-upstream origin backport-3198-to-8.16
# Go back to the original working tree
cd ../..
# Delete the working tree
git worktree remove .worktrees/backport-8.16

Then, create a pull request where the base branch is 8.16 and the compare/head branch is backport-3198-to-8.16.

[github-actions]

The backport to 8.17 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 working tree
git worktree add .worktrees/backport-8.17 8.17
# Navigate to the new working tree
cd .worktrees/backport-8.17
# Create a new branch
git switch --create backport-3198-to-8.17
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x --mainline 1 0b00127e17e82f919ab246388252131269a4488c
# Push it to GitHub
git push --set-upstream origin backport-3198-to-8.17
# Go back to the original working tree
cd ../..
# Delete the working tree
git worktree remove .worktrees/backport-8.17

Then, create a pull request where the base branch is 8.17 and the compare/head branch is backport-3198-to-8.17.