Only configure relevant things on connected endpoints depending on mode.

[ClausHolbechArista]

• The historic default behavior if mode is not set, is access, since it relied on the EOS default to be access. We should make that more clear, so add access as the default in the schema, and also use it as a default value on the get().
• All the logic here is very "loose". We should be more specific to only generate good useful configs. We can match on mode and build the correct structured configs. Any logic here should be reflected in a user-understandable way on each key in the schema. Like "only applicable when mode is set to access" or similar.

Originally posted by @ClausHolbechArista in #4454 (comment)