Add ci hook for building API docs (step 2/3)

[stacey-gammon]

This PR:

• Sets up ci to run the docs command and check for changes
• Fixes a bug with absolute import paths not being stripped out which resulted in ci always finding changes
• Removes some debug lines because there were a ton of them.
• Pretty prints the JSON

There is one more PR (#92929) that is required to make this work, and it's simply removing api_docs from .gitignore.

If you want to view these docs rendered

1. Clone the elastic-docs repo
2. Edit config/sourced-dev.json and add:

    {
      "type": "file",
      "location": "../kibana/api_docs"
    },

Assuming your kibana is a sibling to the elastic-docs repo and the folder is called kibana.

3. Merge https://github.com/elastic/elastic-docs/pull/260 to have the nav items show up.

4. In your kibana repo, pull down this PR, or, just run node scripts/build_api_docs.

5. Run yarn start in the elastic-docs repo

6. Navigate to localhost:8000 and the Kibana Developer Docs Mission.

[kibanamachine]

💚 Build Succeeded

• continuous-integration/kibana-ci/pull-request
• Commit: b9cafa0
• Storybooks Preview

Metrics [docs]

✅ unchanged

History

• 💔 Build #109577 failed a8c0b32d4b9d14e27ba42de23a58fa20d08446ef
• 💔 Build #109489 failed c74b5402556bddbdd647b34f8ccbcb854eb40bef
• 💔 Build #109456 failed 540248b16b08fadb6e99f07aaecb3c3ad5eb70dd
• 💔 Build #109439 failed 7957e1983bbbdbd12d0c5d4659e47493bc70c165
• 💔 Build #109422 failed a67a5da034325cdd5ae53e2da4730f81fd827438

To update your PR or re-run it, just comment with:
@elasticmachine merge upstream

[kibanamachine]

💚 Backport successful

✅ 7.x / #92940

Successful backport PRs will be merged automatically after passing CI.