Use `modeldb%config` object for importing config mod members in adjoint tests where possible

### Are there any linked Issues or Pull Requests?

_No response_

### Brief description

The `adjoint_tests` app uses the old-school way of global imports of config namelist variables. Now that https://github.com/MetOffice/lfric_core/pull/175 has been merged, we can utilise where possible the `modeldb%config` object to get the values of these variables.

### Further details of the issue.

_No response_

Start by searching the adjoint_tests app for global imports of configuration namelist variables and compare them with the available modeldb%config object introduced by lfric_core PR 175. Update the applicable imports to use modeldb%config, leaving unsupported cases unchanged, and run the adjoint tests to confirm their behavior is preserved.

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