This PR contains code changes to add support for option IsolationLevel at the client level and at the transaction level.
supported methods are(RW and Blind Write):

```
- writeAtLeastOnce
- runTransactionAsync
- runTransaction
- getTransaction
- async getTransaction(from transaction runner class)
```

…request (#2205)

* feat(debugging): implement x-goog-spanner-request-id propagation per request

Implements propagation of the x-goog-spanner-request-id that'll be
propagated for every call. Once an error has been encountered, that
error will have `.requestId` set.

Fixes #2200

* All: update tests

* Address review feedback

* Remove a redundant prefix check for values to skip

* Put TODO in correct place for retries from GAX

* test: add test to verify that request-id is received

* Revert protos/* spurious updates

* Correctly check for ExecuteStreamingSql headers asynchronously in callback not assuming synchronous/procedural completion

---------

Co-authored-by: Knut Olav Løite <[email protected]>

* feat(spanner): support for Multiplexed Session Partitioned Ops

* feat(spanner): add support for snapshot isolation (#2245)

This PR contains code changes to add support for option IsolationLevel at the client level and at the transaction level.
supported methods are(RW and Blind Write):

```
- writeAtLeastOnce
- runTransactionAsync
- runTransaction
- getTransaction
- async getTransaction(from transaction runner class)
```

* refactor

* refactor

* feat(spanner): add support for interval

* skip interval tests only in emulator

* Addressed PR comments

* Added tests for null and undefined values

* fixed lint failure

---------

Co-authored-by: Sagar Agarwal <[email protected]>

This change adds the x-goog-spanner-request-id value that is
sent as a gRPC header, but as a span attribute with the
key `x_goog_spanner_request_id` to aid in better debugging
and correlation.

Updates #2200

Co-authored-by: release-please[bot] <55107282+release-please[bot]@users.noreply.github.com>