RPC (gunicorn) service allow passing logging configuration through a file

We used to pass it as a log configuration file in the static infra (and we still do for winery):

• logging config (is a merge of the two dicts)
• gunicorn entry point

Relevant suggestion [1]

rpc (ongoing work [2]):

• objstorage
• storage
• indexer-storage
• vault
• search
• counters
• scheduler
• graphql
• web
• deposit

[1] swh-apps!39 (comment 173686)

[2] swh/infra/ci-cd/swh-charts!458 (merged)