Add migration for version history

What does this MR do and why?

Migrates version history to the Hugo shortcode version.

Closes #11 (closed)

How to set up and validate locally

1. Configure a local GitLab Docs environment: https://gitlab.com/gitlab-org/technical-writing-group/gitlab-docs-hugo/-/blob/main/doc/setup.md.
2. Checkout this branch
3. Fetch up-to-date content, but don't run any migrations: REMOVE_BEFORE_CLONE=true go run cmd/gldocs/main.go clone
4. Run this migration only: go run cmd/gldocs/main.go migrate history ../gitlab/doc
5. View the diff: git -C ../gitlab diff

Expected result: History items (blockquotes, with list items, that contain specific keywords) are rewritten as Hugo shortcodes, like this:

Before:

> - Introduced in 15.0
> - Deprecated in 17.0

After:

{{< history >}}

- Introduced in 15.0
- Deprecated in 17.0

{{</ history >}}

• Multiple history items on consecutive lines should be grouped into a single {{< history >}} block
• Blockquote markdown character (>) is dropped

We can also test the end-to-end build with the migration:

1. Run the full build process: REMOVE_BEFORE_CLONE=true make clone-docs-projects (runs the initial clones + all migrations)
2. Run the preview server: make view
3. Browse around the site and verify that the History content matches its appearance on the existing site.

Example pages:

• Nanoc: https://docs.gitlab.com/ee/administration/settings/account_and_limit_settings.html#max-attachment-size / Hugo: http://localhost:1313/administration/settings/account_and_limit_settings/#max-attachment-size
• Nanoc: https://docs.gitlab.com/ee/user/ai_experiments/#explain-code-in-the-web-ui-with-code-explanation/ / Hugo: http://localhost:1313/user/ai_experiments/#explain-code-in-the-web-ui-with-code-explanation
• Nanoc: https://docs.gitlab.com/ee/user/application_security/dependency_list/ / Hugo: http://localhost:1313/user/application_security/dependency_list/

Merge request acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this merge request.