bots/collectors/api: make socket file permissions configurable

[monoidic]

By default, tornado.netutil.bind_unix_socket creates socket files with 600 permissions and which have the owner and group of the creating user (intelmq). This does not work well in the common case of the process at the other end of the socket not being a process running as the intelmq user.
This commit adds socket_perms and socket_group configuration parameters to the bot to allow for the file's permissions to be changed.

[kamil-certat]

Thank you for the change! The code looks good. Could you please update the changelog (CHANGELOG.md) and possibly also the Bot's documentation in docs/bots.rst?

[sebix]

Good change, as @kamil-certat said. With docs, it would be good to merge.

[monoidic]

Done. Apologies for the delay

[kamil-certat]

@monoidic In the meantime, we have changed the documentation system. May you merge develop and move your docs changes to the docs/user/bots.md?

[sebix]

I fixed the merge errors (some unrelated changes were part of the PR's commits), now ready for merge after the CI checks pass.

[sebix]

Merging, as reviewed OK by @kamil-certat