Put command access checks on the command level

Checking using `settings.Allowed` is odd. Not all commands are related
to setting configuration settings. Admin commands are coming in the
future, for which this is certainly not the case.

We now do access checks early on (during command processing), so command
handlers can be clean of access checks. If we're inside of a command
handler, the user is privileged to run it.

bot/bot.go

@@ -22,6 +22,7 @@ type Bot struct {
 	domain                  string
 	allowedUsers            []*regexp.Regexp
 	allowedAdmins           []*regexp.Regexp
+	commands                commandList
 	rooms                   sync.Map
 	log                     *logger.Logger
 	lp                      *linkpearl.Linkpearl
@@ -38,7 +39,7 @@ func New(
 	allowedUsers []*regexp.Regexp,
 	allowedAdmins []*regexp.Regexp,
 ) *Bot {
-	return &Bot{
+	b := &Bot{
 		noowner:       noowner,
 		federation:    federation,
 		prefix:        prefix,
@@ -50,6 +51,10 @@ func New(
 		lp:            lp,
 		mu:            map[id.RoomID]*sync.Mutex{},
 	}
+
+	b.commands = b.buildCommandList()
+
+	return b
 }
 
 // Error message to the log and matrix room