Googleapis-artman

This release includes updated gapic-generator (with the fix for Java protobuf dependencies), and also a hacky reference to my branch for Python doc string plugin and to `master` branch of Java resource name plugin. If these two plugins are released with fixes, we'll update Artman to point to their proper PyPI locations. Or not.

Updating and releasing `artman` with the following changes:

- bumping gapic-generator version to 2.4.3
- updating versions of `protoc` for all languages to 3.12.x
- passing `--experimental_allow_proto3_optional` to `protoc` invocations
- updating Go version (to fix a build problem)
- update gRPC tools for Python and Ruby to match the new `protoc` version
- bumping `artman` version to 2.4.3 to match gapic-generator version.

gapic-generator:
- feat: add the last segment when generating names for singleton resoures
- fix: add null check and better error message when referenced resources are not found
- feat: Support extra plugin_args for php bazel rules rules
- feat: support '*' in resource definition
- fix: align text in license
- fix(python): add PROJECT_ID for python-system-test
- fix(PYTHON): update nox file and modernize to new interface

java-protoc-resource-names-plugin:
- feat: add the last segment when generating names for singleton resources
- feat: support * annotation in resource def
- feat: trace up only one level when calculating parent types with singleton resources
- fix: stop generating parseList and toStringList if a multi-pattern resource class has subclasses

Python protoc-docs-plugin:
- fix: wrap message docstring

gapic-generator:
- PHP multi-pattern resource name support.
- Trace up only one level when calculating parent types with singleton resource names

Including the following features from gapic-generator:
- Assign the proto file where the interface is defined when generating samples and tests for arbitrary resource names

Features included:

- feat: set x-goog-user-project header for Ruby
- feat: adds reserved name support for PHP and reserved name tests (https://github.com/googleapis/gapic-generator/pull/3100)
- Update protoc-java-resource-name-plugin (812)