* Initial federation sender -> federation API refactoring
* Move base into own package, avoids import cycle
* Fix build errors
* Fix tests
* Add signing key server tables
* Try to fold signing key server into federation API
* Fix dendritejs builds
* Update embedded interfaces
* Fix panic, fix lint error
* Update configs, docker
* Rename some things
* Reuse same keyring on the implementing side
* Fix federation tests, `NewBaseDendrite` can accept freeform options
* Fix build
* Update create_db, configs
* Name tables back
* Don't rename federationsender consumer for now
* Allow configuring DNS cache
* Update sample configs
* Fix build errors
* Fix time resolution
* Default 5m
* In seconds
* Use WithDNScache
* Correct field name
* Update go.mod/go.sum to matrix-org/gomatrixserverlib#251
* Rename serverkeyapi to signingkeyserver
We use "api" for public facing stuff and "server" for internal stuff.
As the server key API is internal only, we call it 'signing key server',
which also clarifies the type of key (as opposed to TLS keys, E2E keys, etc)
* Convert docker/scripts to use signing-key-server
* Rename missed bits
