Public contributor profile pages

Hello,

The Contributors Committee is working on a new program to recognize
specific contributions (e.g. "volunteered at PGConf.dev 2024" or
"contributed code to PostgreSQL 18"). These would be listed on an
individual contributor's profile. As a step toward that, we are
proposing to add public contributor profile pages.

Attached is a patch set which implements this by:
1) allowing all those with pgo user accounts to edit their
"contributions" (currently only enabled for recognized contributors)
2) adds a public contributor profile view accessible via
postgresql.org/community/contributors/[username]
3) links all recognized contributors on [1] to their public contributor profile

There are quite a few details to work out. A few I know of are:
- How should opting into a public profile work? What about existing
recognized contributors, do we opt them all in automatically? Or just
opt-in Major Contributors since their "Contributions" are already on a
public web page? (see patch 0003)
- How to make the public profile URL scheme work for contributors who
do not have a pgo user account? Or should it work at all?

This is my first real web patch, so I'm sure I did some things in a
non-pgweb-idiomatic (or non web-idiomatic) way and didn't think of
lots of things. I'll probably need lots of guidance.

- Melanie

[1] https://www.postgresql.org/community/contributors/