CDRIVER-5581: Add missing license attributions

[Julia-Garland]

Added this header:
`/*

• Copyright 2018-present MongoDB Inc.
• Licensed under the Apache License, Version 2.0 (the "License");
• you may not use this file except in compliance with the License.
• You may obtain a copy of the License at
• http://www.apache.org/licenses/LICENSE-2.0
• Unless required by applicable law or agreed to in writing, software
• distributed under the License is distributed on an "AS IS" BASIS,
• WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
• See the License for the specific language governing permissions and
• limitations under the License.
  */`

To the files:

• mongoc-ts-pool-private.h
• mongoc-opts-private.h
• common/common-macros-private.h

[eramongodb]

LGTM with remaining suggestion applied.