Stability: OS signals

[hug-dev]

Definition: OS signals should still have the same behaviour in future stable Parsec versions.
Enforcement: Signal handlers must not be removed in Parsec.

Enforcement Check

Parsec currently answers to SIGTERM and SIGKILL. Those signals should still have the same behaviour on Parsec for future new versions.

This can only be checked via testing/code review. We can also add warnings in the code, move the relevent files in different modules.

Testing

For testing, those signals should be exerced for different versions of Parsec.

[hug-dev]

All the existing signals should be tested and new tests should be created for the ones added.
Can also do the code separation thing as described in #392

[hug-dev]

Parsec responds to three signals:

• SIGINT and SIGTERM: gracefully terminates it
• SIGHUP: reload the configuration

Those signals are tested in the CI file. The whole main.rs file will be put under CODEOWNERS so that it covers both this issue and #396