This removes the current default of checking for membership of the admin
or admins group and makes it required to explicitly configure which
groups should grant admin access, if any.
Relying on the implicit default of admin or admins is potentially
dangerous as that group may contain a different subset of people that we
may wish to grant admin access to GtS. This is probably not an issue for
a single-person instance, but for a community instance different admin
groups may exist in an OIDC provider for different applications.
I'm explicitly opting for not defaulting the value of oidc-admin-groups
to admin,admins because I think it's better for those things to be
explicitly configured.
* [feature] overhaul the oidc system
this allows for more flexible username handling and prevents account
takeover using old email addresses
* [feature] add migration path for old OIDC users
* [feature] nicer error reporting for users
* [docs] document the new OIDC flow
* [fix] return early on oidc error
* [docs]: add comments on the finalization logic
* start pulling out + replacing urfave and config
* replace many many instances of config
* move more stuff => viper
* properly remove urfave
* move some flags to root command
* add testrig commands to root
* alias config file keys
* start adding cli parsing tests
* reorder viper init
* remove config path alias
* fmt
* change config file keys to non-nested
* we're more or less in business now
* tidy up the common func
* go fmt
* get tests passing again
* add note about the cliparsing tests
* reorganize
* update docs with changes
* structure cmd dir better
* rename + move some files around
* fix dangling comma
