[feature] include local_only in update_credentials

[technicat]

Is your feature request related to a problem ?

all the post settings in gotosocial are saveable (sensitive, privacy, content_type, interaction_policy, language) except local_only, so this is noticeable in my client as the settings are reflected in the post composer and the local_only setting does not persist in the same manner as the others

Describe the solution you'd like.

include local_only as a parameter to update_credentials, perhaps in the same manner as status_content_type (in a source field)

Describe alternatives you've considered.

I could save it as app date with Swift AppStorage but that would differ from the instance persistance of the other settings

Additional context.

this is how the post settings appear in gotosocial on my client fedicat (https://fedicat.com/)