Replace "borg" connection manager with thread safe db pool

[chicco785]

Pools are not offered in the basic driver of crate and psql. It would be good to explore a proper db pool.

Originally posted by @chicco785 in #373 (comment)

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Stale issue message

[daminichopra]

Hi @chicco785 @c0c0n3 , Please assign this issue to me if no one is working on it.
Also , Shall I take reference of this comment for further fix of this issue?

Thank You.

[c0c0n3]

Hi @daminichopra thanks for offering to work on this. Please read through the comments to crate/crate-python#407. I think one option we should consider is to swap out pg8000 for Psycopg in the Postgres translator. Then see if Psycopg would work with Crate too, since it looks like Crate should support the PG wire protocol quite well these days?