Set SWH_MAIN_PACKAGE and SWH_SENTRY_ENVIRONMENT for all services

(these variables are independent from each other, but I'm putting them both in the same task as it's probably less work to handle them both at once)

It should be set the same way we currently have SWH_SENTRY_DSN.

SWH_MAIN_PACKAGE names must be dotted package names (swh.indexer, swh.storage, etc.)

Choosing SWH_SENTRY_ENVIRONMENT names are left to the implementer of this task, but I suggest production and staging, as they match both our terminology and Sentry's.

https://docs.sentry.io/workflow/releases/?platform=python

https://docs.sentry.io/enriching-error-data/environments/?platform=python

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Migrated from T2181 (view on Phabricator)