Adds API arguments and functions for setting a default isolation level and an
isolation level per transaction.

Support for specifying the isolation level using SQL commands will be added
in a follow-up PR.

* fix: improve client-side regex statement parser

The client-side regex-based statement parser contained multiple minor errors, like:
- BEGIN would match any string as BEGIN TRANSACTION (including stuff like `BEGIN foo`)
- COMMIT and ROLLBACK had the same problem as BEGIN.
- Mismatches were reported as UPDATE. They are now returned as UNKNOWN.
- DLL missed the ANALYZE keyword

* 🦉 Updates from OwlBot post-processor

See https://github.com/googleapis/repo-automation-bots/blob/main/packages/owl-bot/README.md

---------

Co-authored-by: Owl Bot <gcf-owl-bot[bot]@users.noreply.github.com>

* feat: add SQL statement for egin transaction isolation level

Adds an additional option to the `begin [transaction]` SQL statement to
specify the isolation level of that transaction. The following format is
now supported:

```
{begin | start} [transaction] [isolation level {repeatable read | serializable}]
```

* test: add test for invalid isolation level

* chore(python): remove noxfile.py from templates

Source-Link: googleapis/synthtool@7765802
Post-Processor: gcr.io/cloud-devrel-public-resources/owlbot-python:latest@sha256:25de45b58e52021d3a24a6273964371a97a4efeefe6ad3845a64e697c63b6447

* 🦉 Updates from OwlBot post-processor

See https://github.com/googleapis/repo-automation-bots/blob/main/packages/owl-bot/README.md

* revert

* remove replacements in owlbot.py

* exclude noxfile.py from gapic-generator-python

---------

Co-authored-by: Owl Bot <gcf-owl-bot[bot]@users.noreply.github.com>
Co-authored-by: Anthonios Partheniou <partheniou@google.com>

* feat: add sample for pre-split feature

* build error fixes

* build failure fixes

* build fixes

* lint fixes

* fixes lint

* fixed the build error

* fixed the build error

* chore: fix positional argument issue

Signed-off-by: Sri Harsha CH <sriharshach@google.com>

* fixed the index test case

* added comment on the splits for idex keys

* fixed indent

* lint fixes

* lint fixes

* chore: tests fix

Signed-off-by: Sri Harsha CH <sriharshach@google.com>

* chore: update sample to not change editions due to failing test case

Signed-off-by: Sri Harsha CH <sriharshach@google.com>

---------

Signed-off-by: Sri Harsha CH <sriharshach@google.com>
Co-authored-by: Sri Harsha CH <sriharshach@google.com>
Co-authored-by: Sri Harsha CH <57220027+harshachinta@users.noreply.github.com>

Signed-off-by: Sri Harsha CH <sriharshach@google.com>

* feat(spanner): add interval type support

* 🦉 Updates from OwlBot post-processor

See https://github.com/googleapis/repo-automation-bots/blob/main/packages/owl-bot/README.md

* fix test

* fix build

* 🦉 Updates from OwlBot post-processor

See https://github.com/googleapis/repo-automation-bots/blob/main/packages/owl-bot/README.md

* incorporate suggestions

* 🦉 Updates from OwlBot post-processor

See https://github.com/googleapis/repo-automation-bots/blob/main/packages/owl-bot/README.md

---------

Co-authored-by: Owl Bot <gcf-owl-bot[bot]@users.noreply.github.com>

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