[docs] Migrate docs from AsciiDoc to Markdown

[colleenmcginnis]

Migrate docs from AsciiDoc to Markdown. The preview can be built after #2450 is merged.

[github-actions]

Documentation changes preview: https://ecs_bk_2451.docs-preview.app.elstc.co/diff

[mjwolf]

@colleenmcginnis There were some changes made to ECS after the docs freeze. Are the new docs generated from the latest main branch? Most of the changes are to the schema files, so I think docs should get the latest changes from automatic generation.

One other thing I saw is docs/release-notes/8.17.asciidoc is not deleted in this PR. It was added to main recently, so it should be deleted with the other asciidoc files.

[colleenmcginnis]

Are the new docs generated from the latest main branch?

No. They were generated at the start of the docs freeze.

Most of the changes are to the schema files, so I think docs should get the latest changes from automatic generation.

Is the automatic generation still creating AsciiDoc files? If so, they will need to be updated to Markdown.

[colleenmcginnis]

Most of the changes are to the schema files, so I think docs should get the latest changes from automatic generation.

Is the automatic generation still creating AsciiDoc files? If so, they will need to be updated to Markdown.

I resolved the merge conflicts. Do these look like the only updates that would have been made? 5cb6754?file-filters%5B%5D=.md&show-deleted-files=true&show-viewed-files=true

[colleenmcginnis]

@mdbirnstiehl this should fix the inbound link validation error: elastic/apm-agent-dotnet#2563

[mdbirnstiehl]

@mjwolf Could you help us out here on the test failing. Also, do you know if there were any additional changes made other than the ones mentioned by @colleenmcginnis?