Add networking reference link

[ChrisChinchilla]

• addresses Build manual page does not explain the --network argument docs#16890

- What I did

Added a link to --networking flag as requested in this issue docker/docs#16890

Made it an "external" link for better usage in multiple locations.

[codecov-commenter]

Codecov Report

Merging #4166 (64e9cad) into master (21682eb) will not change coverage.
The diff coverage is n/a.

Additional details and impacted files

@@ Coverage Diff @@## master #4166 +/- ##
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Coverage 59.64% 59.64% =======================================
Files 287 287 Lines 24771 24771 =======================================
Hits 14774 14774 Misses 9111 9111 Partials 886 886 

[akerouanton]

LGTM

[thaJeztah]

left a comment (I can catch up with you if needed)

[thaJeztah]

This table is actually generated from the source code (I thought we had a verify step for this one to check it, but looks like it doesn't flag this 🤔). The table in markdown is only used on GitHub (and generated from the YAML properties on docs.docker.com).

What I think we need here instead is to either add a section for this option further down (having the right anchor tag to match the flag name), and add the link for details in there, or perhaps we need to add a link to the buildx build documentation as alternative link (if that page does have a description).

[ChrisChinchilla]

Hmm, there don't actually appear to be many sections for more explanation in this doc. Is there any reason we can't add links to code comments? Or we'd just rather not?

[thaJeztah]

Looks like buildx build also doesn't have a flag description for this, so we probably need to add one on this page (or both, if there's differences between BuildKit's support for --network and non-buildkit (see moby/moby#40379))

@crazy-max do you know from the top of your head if BuildKit now has full feature-parity on --network ?

[ChrisChinchilla]

@thaJeztah and @crazy-max Turns out my last change was linking people to the wrong place anyway and digging more into this it seems that --network is basically the only non-experimental flag with the build/buildx disparity. So I think this latest change is correct now

[thaJeztah]

Rebased, and squashed the commits

[thaJeztah]

LGTM if CI is happy