leaudio: Fix resume on LocalSink

Instead of checking if resume is expected, we should check if it is
allowed. That means, we should not expect configuration being already
cached for given context, but rather we should check if there is a
valid configuration for the give context.

Without the fix if metadata update is not sent before resume, we might
end up with stream being not establish as cache config might not exist
yet.

Note that if there was never MetadataUpdate called before the Resume,
stream still will not be created.

Bug: 303287030
Test: atest bluetooth_le_audio_client_test
Tag: #feature
Change-Id: I26042bdd292fc6f74c48b069f1cc0277fee2a8b5