Restrict implicit id mapping to document types

[DragonFSKY]

Closes #3351

This PR introduces an opt-in setting on MongoMappingContext to restrict implicit id to _id mapping to types annotated with @Document.

The default remains unchanged to preserve the existing behavior for compatibility. Explicit @Id mappings continue to be recognized regardless of the owning type.

The change includes coverage for:

• persistent property id detection
• read/write mapping of root and nested values
• query mapping of nested id paths
• update mapping of nested id paths and values

Tested with:

./mvnw -s settings.xml -pl spring-data-mongodb clean test -Dtest=BasicMongoPersistentPropertyUnitTests,MappingMongoConverterUnitTests,QueryMapperUnitTests,UpdateMapperUnitTests

Checklist:

• You have read the Spring Data contribution guidelines.
• You use the code formatters provided by the project and have not submitted unrelated formatting changes.
• You submit test cases that back your changes.
• You added yourself as author in the headers of the classes you touched.