[Task]: Add MetadataSpannerConfig class for generating SpannerConfig for accessing change stream metadata database

### What needs to happen?

created from https://github.com/apache/beam/pull/25108#issuecomment-1400709831:

When reading from change streams there are two databases involved, 1) the primary database that contains the change stream, and 2) a metadata database (maintained by Beam) that holds partition progress state so a job can be restarted and pick up where it left off. To create a spanner config to access the metadata database, the following pattern is used:
```
SpannerConfig metadataConfig = spannerConfig.toBuilder()
.setInstanceId(metadataInstanceId)
.setDatabaseId(metadataDatabaseId)
.build();
```
The metadata config (`metadataConfig`) is initialized using the primary database config (`spannerConfig`) since most of the fields are the same and then the ones that are different get overwritten. With the Fine-Grained Access Control project, we've added a new config field _databaseRole_ that should only be set for primary database access. Unfortunately the pattern above blindly copies this field to the metadata config. A better approach would be to write a metadata config create function that copies a whitelisted set of fields from the primary config and leaves all of the other fields empty.

### Issue Priority

Priority: 2 (default / most normal work should be filed as P2)

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