Add GitLab API clients to the documentation

What does this MR do?

Add the API client libraries to the REST API docs, that were previously linked on the marketing website on the Alliance Partners page.

1. Reviewed all linked projects for activity
2. Created sections by language
3. Added introduction text, with pointing users to community resources

Integrations is owned by groupimport and integrate in the devopsmanage stage.

Old changes

Click to expand

This MR is to add our API clients to our Docs > Integrations pages. These listings were previously on the Alliance Partners page but we are removing the API & CLI client integration categories from this page and would like to relocate them here.

Update 2023-08-05 @dnsmichi remove the CLI portions - we have the GitLab CLI officially since last year: https://docs.gitlab.com/ee/editor_extensions/gitlab_cli/index.html

Related issues

gitlab-com/marketing/digital-experience/buyer-experience#1825 (comment 1270686775)

Author's checklist

• Optional. Consider taking the GitLab Technical Writing Fundamentals course.
• Follow the:
  • Documentation process.
  • Documentation guidelines.
  • Style Guide.
• If you're adding or changing the main heading of the page (H1), ensure that the product tier badge is added.
• If you are a GitLab team member, request a review based on:
  • The documentation page's metadata.
  • The associated Technical Writer.

If you are a GitLab team member and only adding documentation, do not add any of the following labels:

• ~"frontend"
• ~"backend"
• ~"type::bug"
• ~"database"

These labels cause the MR to be added to code verification QA issues.

Reviewer's checklist

Documentation-related MRs should be reviewed by a Technical Writer for a non-blocking review, based on Documentation Guidelines and the Style Guide.

If you aren't sure which tech writer to ask, use roulette or ask in the #docs Slack channel.

• If the content requires it, ensure the information is reviewed by a subject matter expert.
• Technical writer review items:
  • Ensure docs metadata is present and up-to-date.
  • Ensure the appropriate labels are added to this MR.
  • Ensure a release milestone is set.
  • If relevant to this MR, ensure content topic type principles are in use, including:
    • The headings should be something you'd do a Google search for. Instead of Default behavior, say something like Default behavior when you close an issue.
    • The headings (other than the page title) should be active. Instead of Configuring GDK, say something like Configure GDK.
    • Any task steps should be written as a numbered list.
    • If the content still needs to be edited for topic types, you can create a follow-up issue with the docs-technical-debt label.
• Review by assigned maintainer, who can always request/require the reviews above. Maintainer's review can occur before or after a technical writer review.