feat(coderd): add company logo when available for email notifications (#14935)

This PR aims to close #14253 

We keep the default behavior using the Coder logo if there's no logo
set.
Otherwise we want to use the logo based on the URL set in appearance.

---------

Co-authored-by: defelmnq <yvincent@coder.com>

coderd/notifications/manager_test.go

@@ -5,6 +5,7 @@ import (
 	"encoding/json"
 	"sync/atomic"
 	"testing"
+	"text/template"
 	"time"
 
 	"github.com/google/uuid"
@@ -210,8 +211,8 @@ type santaHandler struct {
 	nice    atomic.Int32
 }
 
-func (s *santaHandler) Dispatcher(payload types.MessagePayload, _, _ string) (dispatch.DeliveryFunc, error) {
-	return func(ctx context.Context, msgID uuid.UUID) (retryable bool, err error) {
+func (s *santaHandler) Dispatcher(payload types.MessagePayload, _, _ string, _ template.FuncMap) (dispatch.DeliveryFunc, error) {
+	return func(_ context.Context, _ uuid.UUID) (retryable bool, err error) {
 		if payload.Labels["nice"] != "true" {
 			s.naughty.Add(1)
 			return false, xerrors.New("be nice")