[feature] User muting (#2960)

* User muting

* Address review feedback

* Rename uniqueness constraint on user_mutes to match convention

* Remove unused account_id from where clause

* Add UserMute to NewTestDB

* Update test/envparsing.sh with new and fixed cache stuff

* Address tobi's review comments

* Make compiledUserMuteListEntry.expired consistent with UserMute.Expired

* Make sure mute_expires_at is serialized as an explicit null for indefinite mutes

---------

Co-authored-by: tobi <tobi.smethurst@protonmail.com>

testrig/testmodels.go

@@ -3392,6 +3392,11 @@ func NewTestFilterStatuses() map[string]*gtsmodel.FilterStatus {
 	}
 }
 
+func NewTestUserMutes() map[string]*gtsmodel.UserMute {
+	// Not currently used.
+	return map[string]*gtsmodel.UserMute{}
+}
+
 // GetSignatureForActivity prepares a mock HTTP request as if it were going to deliver activity to destination signed for privkey and pubKeyID, signs the request and returns the header values.
 func GetSignatureForActivity(activity pub.Activity, pubKeyID string, privkey *rsa.PrivateKey, destination *url.URL) (signatureHeader string, digestHeader string, dateHeader string) {
 	// convert the activity into json bytes