release notes for v0.37.0

[rvan...@google.com]

• blob

  • s3blob: Support S3 server side encryption headers for Write and Copy.
  • gcsblob: Ensure driver sets Content-Type auto-detection properly.

• pubsub

  • azpubsub: Ensure 401s are not retryable.
  • azpubsub: Allow configuring max_recv_batch_size in via URL.
  • mongodocstore: Fix error when calling the update function with no 'set' operations.

• docstore

  • all: Add Offset method, useful for pagination