Use read/write connection modes to the compute-db

[mcucchi9]

This PR implements:

• usage of two different connection modes (read and write) to the compute-db;
• retry on write compute-db hostname if NoSuchJob is returned by get_job_from_broker_db

Requires:

• https://github.com/ecmwf-projects/cads-broker/tree/implement-read-and-write

[FussyDuck]

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1 out of 2 committers have signed the CLA.

✅ mcucchi9
❌ francesconazzaro
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