Remove signac Support Email

[mikemhenry]

We have the signac-support@umich.edu email linked in a few spots across signac & friends.

$ rg --files-with-matches "signac-support@umich.edu"
signac-docs/CODE_OF_CONDUCT.md
signac-docs/docs/source/community.rst
signac/setup.py
signac/CODE_OF_CONDUCT.md
signac/doc/support.rst
signac-dashboard/CODE_OF_CONDUCT.md
signac-flow/CODE_OF_CONDUCT.md
signac-flow/setup.py
signac-flow/doc/support.rst
signac-flow/doc/supported_environments.rst
signac-dashboard/doc/support.rst

Really the only spot I'm not sure how we want to replace the email is in the setup.py for signac & signac-flow:
maintainer_email="signac-support@umich.edu"

Do we want to replace it with a different email or just drop that bit of metadata?

@b-butler @bdice @cbkerr

[bdice]

Hmm. I also don't want to remove an email from the Code of Conduct. Let's keep the email alive (@cbkerr, please ask admins to add you there) but redirect the following pages in our docs to Slack:

signac-docs/docs/source/community.rst
signac/doc/support.rst
signac-flow/doc/support.rst
signac-flow/doc/supported_environments.rst
signac-dashboard/doc/support.rst

[mikemhenry]

Sounds good! I was thinking that the email had more use that we thought it did and wanted to make sure that we don't let it die.

This could be an opportunity to move the email to a google group that we control, but that is something we can talk about next time.