Add support for configuring user whitelisting

This does not do anything useful just yet.
It will be hooked to access control checks later on.

Wildcards are converted to regular expressions, because it was simpler
to do that than to write (or include) some ugly wildcard matcher library.
It also provides more flexibility, should we wish to use it later.
Regular expressions should also work well performance-wise.

We compile wildcards to regexes early on (during configuration
processing) and fail if we detect a bad pattern. This is meant to
catch various problems (typos or other mistakes) that could happen.

For this to work, configuration building had to be redone, since it can
now return an error. This may be useful in the future for validating
other configuration settings.

Related to https://gitlab.com/etke.cc/postmoogle/-/issues/1

bot/bot.go

@@ -3,6 +3,7 @@ package bot
 import (
 	"context"
 	"fmt"
+	"regexp"
 	"sync"
 
 	"github.com/getsentry/sentry-go"
@@ -19,6 +20,7 @@ type Bot struct {
 	federation              bool
 	prefix                  string
 	domain                  string
+	allowedUsers            []*regexp.Regexp
 	rooms                   sync.Map
 	log                     *logger.Logger
 	lp                      *linkpearl.Linkpearl
@@ -26,15 +28,16 @@ type Bot struct {
 }
 
 // New creates a new matrix bot
-func New(lp *linkpearl.Linkpearl, log *logger.Logger, prefix, domain string, noowner, federation bool) *Bot {
+func New(lp *linkpearl.Linkpearl, log *logger.Logger, prefix, domain string, noowner, federation bool, allowedUsers []*regexp.Regexp) *Bot {
 	return &Bot{
-		noowner:    noowner,
-		federation: federation,
-		prefix:     prefix,
-		domain:     domain,
-		rooms:      sync.Map{},
-		log:        log,
-		lp:         lp,
+		noowner:      noowner,
+		federation:   federation,
+		prefix:       prefix,
+		domain:       domain,
+		allowedUsers: allowedUsers,
+		rooms:        sync.Map{},
+		log:          log,
+		lp:           lp,
 	}
 }