Honor OPENSSL_FORCE_FIPS_MODE in Docker sshd configuration

What does this MR do?

The upgrade to the Ubuntu 24.04 image caused the OpenSSH server to stop working on FIPS hosts. As described in https://github.com/dotnet/dotnet-docker/issues/5849#issuecomment-2324943811 Ubuntu now requires that the OpenSSL FIPS libraries are used if FIPS is enabled in the kernel. This causes sshd not to start and log PRNG is not seeded error messages in /var/log/gitlab/sshd/current.

Now if you want to mix and match FIPS and non-FIPS libraries, you have to explicitly set OPENSSL_FORCE_FIPS_MODE=0. While mixing flavors isn't ideal here, it worked before, and we need to provide customers with a way to work around the issue until a better solution is implemented.

This commit detects if OPENSSL_FORCE_FIPS_MODE is set in the environment and propagates it to the GitLab-managed OpenSSH server, sshd.

Related issues

Relates to https://gitlab.com/gitlab-com/request-for-help/-/issues/2920

Checklist

See Definition of done.

For anything in this list which will not be completed, please provide a reason in the MR discussion.

Required

• MR title and description are up to date, accurate, and descriptive.
• MR targeting the appropriate branch.
• Latest Merge Result pipeline is green.
• When ready for review, MR is labeled workflowready for review per the Distribution MR workflow.

For GitLab team members

If you don't have access to this, the reviewer should trigger these jobs for you during the review process.

• The manual Trigger:ee-package jobs have a green pipeline running against latest commit.
• If config/software or config/patches directories are changed, make sure the build-package-on-all-os job within the Trigger:ee-package downstream pipeline succeeded.
• If you are changing anything SSL related, then the Trigger:package:fips manual job within the Trigger:ee-package downstream pipeline must succeed.
• If CI configuration is changed, the branch must be pushed to dev.gitlab.org to confirm regular branch builds aren't broken.

Expected (please provide an explanation if not completing)

• Test plan indicating conditions for success has been posted and passes.
• Documentation created/updated.
• Tests added.
• Integration tests added to GitLab QA.
• Equivalent MR/issue for the GitLab Chart opened.
• Validate potential values for new configuration settings. Formats such as integer 10, duration 10s, URI scheme://user:passwd@host:port may require quotation or other special handling when rendered in a template and written to a configuration file.