MM-58038: Use context to call master for DeletePost (#27098)

Calling app.DeletePost immediately after creating a post
is susceptible to replica lag because we were calling the
replica to check for the post.

We fix this by passing a context to always query master.

https://mattermost.atlassian.net/browse/MM-58038

```release-note
NONE
```

server/channels/store/sqlstore/post_store.go

@@ -833,7 +833,7 @@ func (s *SqlPostStore) Get(ctx context.Context, id string, opts model.GetPostsOp
 	return pl, nil
 }
 
-func (s *SqlPostStore) GetSingle(id string, inclDeleted bool) (*model.Post, error) {
+func (s *SqlPostStore) GetSingle(rctx request.CTX, id string, inclDeleted bool) (*model.Post, error) {
 	query := s.getQueryBuilder().
 		Select("p.*").
 		From("Posts p").
@@ -855,7 +855,7 @@ func (s *SqlPostStore) GetSingle(id string, inclDeleted bool) (*model.Post, erro
 	}
 
 	var post model.Post
-	err = s.GetReplicaX().Get(&post, queryString, args...)
+	err = s.DBXFromContext(rctx.Context()).Get(&post, queryString, args...)
 	if err != nil {
 		if err == sql.ErrNoRows {
 			return nil, store.NewErrNotFound("Post", id)

server/channels/store/sqlstore/team_store.go

@@ -945,7 +945,7 @@ func (s SqlTeamStore) UpdateMember(rctx request.CTX, member *model.TeamMember) (
 }
 
 // GetMember returns a single member of the team that matches the teamId and userId provided as parameters.
-func (s SqlTeamStore) GetMember(ctx request.CTX, teamId string, userId string) (*model.TeamMember, error) {
+func (s SqlTeamStore) GetMember(rctx request.CTX, teamId string, userId string) (*model.TeamMember, error) {
 	query := s.getTeamMembersWithSchemeSelectQuery().
 		Where(sq.Eq{"TeamMembers.TeamId": teamId}).
 		Where(sq.Eq{"TeamMembers.UserId": userId})
@@ -956,7 +956,7 @@ func (s SqlTeamStore) GetMember(ctx request.CTX, teamId string, userId string) (
 	}
 
 	var dbMember teamMemberWithSchemeRoles
-	err = s.DBXFromContext(ctx.Context()).Get(&dbMember, queryString, args...)
+	err = s.DBXFromContext(rctx.Context()).Get(&dbMember, queryString, args...)
 	if err != nil {
 		if err == sql.ErrNoRows {
 			return nil, store.NewErrNotFound("TeamMember", fmt.Sprintf("teamId=%s, userId=%s", teamId, userId))