Dynamically download release information from Bodhi

[owtaylor]

fedora/release_info.py is a liability, because when things change - e.g., a new Flatpaks release is added in Fedora - the indexer breaks in a hard-to-notice fashion.

We can get the same information directly from Bodhi using the https://bodhi.fedoraproject.org/releases/?exclude_archived=1

Endpoint. Basic idea is:

• Add bodhi_query.py: refresh_updates()
• Have that cache a JSON-object in redis like:

[
{
   "name": "F34F",
   "content_type": "flatpak",
   "branch": "f34"
}
]

• Call refresh_* updates() once per update cycle, then load and use it where we currently use release_info.py. (Probably pass the loaded result as a parameter to bodhi_update.py:_query_updates() to reduce redis round-trips.)