Fix custom CA cert support

What does this MR do?

Fix support for custom CA certificates

The main problem was that the proper java certificate store was never found due to the JAVA_HOME env var not being properly set before importing custom ca certs. This fixes things by adding certificates to all stores found in the asdf java installs (currently java 8 and java 11).

The reasoning for searching for the cert stores is that java 8 and java 11 both have different paths. Java 8 puts it within a jre dir that doesn't exist for the java 11 install.

Add better tests for custom CA certificates

https://gitlab.com/gitlab-org/security-products/tests/java-maven/-/pipelines/431355913 shows the new test failing for the latest spotbugs image and the latest pipeline run for this MR shows that it now passes!

What are the relevant issue numbers?

• gitlab-org/gitlab#296921 (closed)
• gitlab-org/gitlab#342561 (closed)

Does this MR meet the acceptance criteria?

• Changelog entry added
• Documentation created/updated for GitLab EE, if necessary
• Documentation created/updated for this project, if necessary
• Documentation reviewed by technical writer or follow-up review issue created
• Tests added for this feature/bug
• Job definition updated, if necessary
  • Auto-DevOps template (also in CE)
  • Job definition example
  • CI Templates (to be removed)
  • Vendored CI Templates (also in CE)
• Conforms to the code review guidelines
• Conforms to the Go guidelines
• Security reports checked/validated by reviewer