Provide bridges of the configure transport by default on email distributor

meskiorequested to merge
meskio/bridgedb:email_default_obfs4 into main

The default command 'get bridges' now now answers with 'DEFAULT_TRANSPORT' (obfs4 for now) bridges. Adding a new command 'get vanilla' to be able to get vanilla bridges if this is really the intent of the requester.

Closes: #40019 (closed)

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