Allow services tagged as 'encoder' to opt out of inclusion in the serializer.formats container paramater

Problem/Motivation

When adding new encoders, it doesn't make sense for these encoders to always become available for use as formats in the rest system. Some examples:

• #2841027: JSON API format should only be used on JSON API routes, but can currently also be used for REST resources →
• #2978758: Add support for a CSV encoder in core →

Proposed resolution

Allow an optional additional item of metadata that excludes services tagged 'encoder' from being included in the list formats in 'serializer.formats'.

Remaining tasks

User interface changes

API changes

Data model changes