Add --socket=gpg-agent

[bl00mber]

close #2301

[Erick555]

In previous attempt there was problem with gnupg parent folder that contains sockets - gpg requires it to have 700 unix permissions while bwrap by default uses 755. Are you sure it's no longer a concern? Since then bwrap gained way to override permissions but it needs to be used.

[bl00mber]

@Erick555 I've managed to run gpg-agent dependent application tasks from flatpak, as well as gpg

[Erick555]

Yeah, the permission problem seems to be fixed since version 1.11

[bl00mber]

Can you merge @mwleeds @alexlarsson

[mwleeds]

If you add a new socket you need to update the man pages for the build-finish, build, override, and run commands. Ideally there should be a unit test as well if it's technically feasible.

[bl00mber]

I updated manpages @mwleeds not sure how to make a socket test though, it seems there are no other socket that is covered by test of its direct functionality

[mwleeds]

Can you squash the three commits into one? Here is how to do it:

1. git rebase -i a421e1cc6f78649ea75118404d07b410a7f13e1d^
2. Edit the two subsequent commits to have "fixup" rather than "pick" as the first word
3. Save and exit the editor
4. Force push with git push -f <remote_name> add-socket-gpg-agent, but use the actual remote name

[bl00mber]

@mwleeds done