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Adds a simple configuration option that allows the user to select which tls cipher he wishes to use.
One caveat is that currently only SHA256 ciphers are supported; this in effect means that currently
the cipher TLS_AES_256_GCM_SHA384 is not supported.

This PR also adds a config option to make bareos tell openssl to use ktls if it can.

Please check

• Short description and the purpose of this PR is present above this paragraph
• Your name is present in the AUTHORS file (optional)

If you have any questions or problems, please give a comment in the PR.

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Checklist for the reviewer of the PR (will be processed by the Bareos team)

Make sure you check/merge the PR using devtools/pr-tool to have some simple automated checks run and a proper changelog record added.

General

• Is the PR title usable as CHANGELOG entry?
• Purpose of the PR is understood
• Commit descriptions are understandable and well formatted
• Check backport line
• Required backport PRs have been created

Source code quality

• Source code changes are understandable
• Variable and function names are meaningful
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Tests

• Decision taken that a test is required (if not, then remove this paragraph)
• The choice of the type of test (unit test or systemtest) is reasonable
• Testname matches exactly what is being tested
• On a fail, output of the test leads quickly to the origin of the fault