add default branches that are ignored by smithy for uploads

[beckermr]

Right now, one can set an appropriate key in the conda-forge.yml to have smithy only do uploads for certain branches. This is useful, but @jaimergp and I discussed a separate scheme that we think could be a nice default and enable some new things. The idea is to always disallow uploads from anything that matches the following globs/regex:

• _* (i.e., any branch that starts with an underscore)
• (^[a-z,A-Z,_,\-,0-9]+)(-patch-)([0-9]+$) (i.e., any branch that matches the pattern of default GH branch names for edits in the UI, <username>-patch-<number>.
• any branch that matches the default branch name for PR reversions (need to look this up)

If we moved to this system, then we'd avoid common user errors of uploads happening when they do not fork the feedstock and we could use branches that start with _ for automated tasks like rerendering.

Thoughts @conda-forge/core?

[h-vetinari]

Why not do an allowlist instead of a blocklist? Something like main|dev|rc + ^v?[\d\.]+(\.x)?$; or maybe just main and enable extending that list through conda-forge.yml?

In any case, an allowlist seems way more waterproof than chasing holes in our blocklists to me.

[beckermr]

I don't care how it is phrased so happy with whatever in terms of allow vs reject lists.

One vote in favor of an expanded reject list is that if we instated allow lists we'd probably break existing feedstocks at some point.

The big point here, however, is that our current default of allowing everything is not as useful as several other possible default choices and I think we should change it.