yaml: add processing for internal links, and tests

[dvdksn]

Relates to:

• Reference docs URL scheme docs#19370
• docs: update link targets cli#4866
• docs: use absolute links and update link targets buildx#2253

Adds a preprocessing step for links when generating yaml,
reformatting internal, relative links between CLI docs.

Internal links between docs have some variation of the following syntax:

• [linktext](cmd_subcmd.md)
• [linktext](./cmd_subcmd.md)

Links may also contain an optional anchor:

• [linktext](cmd_subcmd.md#anchor)
• [linktext](./cmd_subcmd.md#anchor)

The added preprocessing step rewrites these links in the yaml conversion to:

• [linktext](/reference/cli/docker/cmd/subcmd/)
• [linktext](/reference/cli/docker/cmd/subcmd/#anchor)

Also added tests:

• for the above case, and
• for stripping https://docs.docker.com from links (preexisting)

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (e1a3957) 67.36% compared to head (d13ddac) 69.58%.
Report is 2 commits behind head on main.

Additional details and impacted files

@@ Coverage Diff @@## main #49 +/- ##
==========================================
+ Coverage 67.36% 69.58% +2.22% 
==========================================
Files 4 4 Lines 576 434 -142 ==========================================
- Hits 388 302 -86 + Misses 132 76 -56 
Partials 56 56 

☔ View full report in Codecov by Sentry.
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[dvdksn]

PTAL @thaJeztah@crazy-max@tonistiigi

[dvdksn]

ugh, I just realized this doesnt work in docker/cli because dockerd.md is currently in the same directory as the docker cli reference files, but on docs.docker.com it will be served under a different url path.

[dvdksn]

this one's ready to go I think. I've updated (reverted) the docker/buildx and docker/cli PRs to use relative links again, and used this fork of cli-docs-tool to test them. Worked as expected

[crazy-max]

Thanks LGTM, PTAL @thaJeztah

[dvdksn]

Rebased docker/docs#19370 and it's green now again, so we should be good to go ahead in the following order:

• merge this and tag a new release of cli-docs-tool
• bump cli-docs-tool in docker/cli and docker/buildx
• merge docs: update link targets cli#4866 and docs: use absolute links and update link targets buildx#2253
• backport
• update vendor in Reference docs URL scheme docs#19370
• merge and release

[crazy-max]

LGTM