LE Audio: PACS: Support multiple PAC characteristics

[Thalley]

Is your enhancement proposal related to a problem? Please describe.
Currently we only ever expose a single Sink PAC or Source PAC characteristics in PACS, but the spec states:

When the server supports reception of audio data, the decision to expose all supported PAC records
within a single Sink PAC characteristic or multiple Sink PAC characteristics is left to the implementation.

Describe the solution you'd like
We should allow for multiple PAC characteristics per direction, configurable by a Kconfig. This will also require an API change as the application will need to decide which characteristic to store a specific PAC record in.

Describe alternatives you've considered
N/A

Additional context
Related to #70826