cmd/go: GOCACHEPROG needs real documentation

[aclements]

GOCACHEPROG will be enabled by default in Go 1.24. Currently, the only documentation on this appears to be #59719 (comment), which is quite terse and not completely up-to-date.

We should add a real documentation page on this setting and the protocol, probably to the cmd/go documentation. Once we've done this, we should also update the 1.24 release notes to point to the documentation instead of #59719.

[gabyhelp]

Related Issues

• cmd/go: enable GOCACHEPROG by default #64876 (closed)
• cmd/go: remove note about GOCACHE=off in docs #29681 (closed)
• cmd/go: doc: no official explanation about GOCACHE=off ? #25928 (closed)

_{(Emoji vote if this was helpful or unhelpful; more detailed feedback welcome in this discussion.)}

[gopherbot]

Change https://go.dev/cl/638567 mentions this issue: cmd/go: add "go help gocacheprog" topic

[gopherbot]

Change https://go.dev/cl/638566 mentions this issue: cmd/go: improve GOCACHEPROG types documentation

[gopherbot]

Change https://go.dev/cl/638996 mentions this issue: cmd/go/internal/cacheprog: drop redundant Prog prefixes

[gopherbot]

Change https://go.dev/cl/638995 mentions this issue: cmd/go: move GOCACHEPROG protocol types to their own package

[gopherbot]

Change https://go.dev/cl/638997 mentions this issue: cmd/go: document GOCACHEPROG in go help environment

[gopherbot]

Change https://go.dev/cl/638378 mentions this issue: _content/doc/go1.24: link to in-tree GOCACHEPROG docs