Should cli plugins install to ~/.docker/plugins

[ijc]

This is part of #1661, originally #1564 (comment).

Also for a follow-up bike-shed; wondering if we should change the path to just ~/.docker/plugins (as the daemon won't install plugins in this location, so there should be no real ambiguity there)

In isolation it seems like a sensible suggestion, but there is the global path to consider too, which is (from `docs/extend/cli_plugins.md):

Plugins distributed in packages for system wide installation on
Unix(-like) systems should be installed in either
/usr/lib/docker/cli-plugins or /usr/libexec/docker/cli-plugins
depending on which of /usr/lib and /usr/libexec is usual on that
system. System Administrators may also choose to manually install into
the /usr/local/lib or /usr/local/libexec equivalents but packages
should not do so.

I think in that context there is a greater possibility of confusion with daemon plugins (even if it goes nowhere near anything like those paths, they are not so unambiguous when they are in /usr).

I think the name cli-plugins is the lesser evil compared with having the per-user and per-system directories have different names, so we should leave it alone but I'm happy to be guided by the maintainers.

/cc @thaJeztah @silvin-lubecki @vdemeester (who else?) WDYT? Happy to raise a PR with the change if that is your consensus.

[thaJeztah]

Discussing with @ijc on Slack, and indeed, in a situation where the daemon and cli are both installed on the same host, using just plugins will make things more confusing, so I agree that we should not change

[silvin-lubecki]

I think the more obvious it is, the less issues we'll have with cli plugins. So I'm fine with keeping things as-is 👍

[cpuguy83]

Don't forget rootless mode. Supporting cli plugins totally from a user home directory is definitely a boon here.