examples: unify related CMS examples in README

[JamBalaya56562]

What?

Add missing related CMS examples and sort them.

Why are cms-keystonejs-embedded and cms-strapi lacking?

Because these have only README.md file.

How?

Update with the following text.

- [AgilityCMS](/examples/cms-agilitycms)
- [Builder.io](/examples/cms-builder-io)
- [ButterCMS](/examples/cms-buttercms)
- [Contentful](/examples/cms-contentful)
- [Cosmic](/examples/cms-cosmic)
- [DatoCMS](/examples/cms-datocms)
- [DotCMS](/examples/cms-dotcms)
- [Drupal](/examples/cms-drupal)
- [Enterspeed](/examples/cms-enterspeed)
- [Ghost](/examples/cms-ghost)
- [GraphCMS](/examples/cms-graphcms)
- [Kontent.ai](/examples/cms-kontent-ai)
- [MakeSwift](/examples/cms-makeswift)
- [Payload](/examples/cms-payload)
- [Plasmic](/examples/cms-plasmic)
- [Prepr](/examples/cms-prepr)
- [Prismic](/examples/cms-prismic)
- [Sanity](/examples/cms-sanity)
- [Sitecore XM Cloud](/examples/cms-sitecore-xmcloud)
- [Sitefinity](/examples/cms-sitefinity)
- [Storyblok](/examples/cms-storyblok)
- [TakeShape](/examples/cms-takeshape)
- [Tina](/examples/cms-tina)
- [Umbraco](/examples/cms-umbraco)
- [Umbraco heartcore](/examples/cms-umbraco-heartcore)
- [Webiny](/examples/cms-webiny)
- [WordPress](/examples/cms-wordpress)
- [Blog Starter](/examples/blog-starter)

CC: @samcx

Adding or Updating Examples

• The "examples guidelines" are followed from our contributing doc https://github.com/vercel/next.js/blob/canary/contributing/examples/adding-examples.md
• Make sure the linting passes by running pnpm build && pnpm lint. See https://github.com/vercel/next.js/blob/canary/contributing/repository/linting.md

[ijjk]

Allow CI Workflow Run

• approve CI run for commit: d2a36bf

Note: this should only be enabled once the PR is ready to go and can only be enabled by a maintainer

[samcx]

Thank you for submitting a PR!