Convert Pub/Sub Schema IO to SchemaTransform

[damccorm]

The output of this task is to refactor sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/pubsub/PubsubSchemaIOProvider.java to extend TypedSchemaTransformProvider.

This task will be separated into four PRs to focus on Read and Write SchemaTransforms and their respective Configurations. See BigQuerySchemaTransformReadProvider and BigQuerySchemaTransformWriteConfiguration as an example design pattern.

Imported from Jira BEAM-14036. Original Jira may contain additional context.
Reported by: laraschmidt.
Subtask of issue #21406

[damccorm]

Unable to assign user @damondouglas. If able, self-assign, otherwise tag @damccorm so that he can assign you. Because of GitHub's spam prevention system, your activity is required to enable assignment in this repo.

[damondouglas]

@damccorm Would you mind to assign me to this task? Thank you for migrating these issues!

[damondouglas]

Associating PR: #17730 to this task.

[damondouglas]

This issue has a new dependency: #22768