The changes of the PR basically make copy and paste easier.

It fixes e.g. a copy and paste problem on install scripts where shell-session
was used as language identifier for pygments instead of sh/shell.

The PR also introduces the sphinx_copybutton extension.
The sphinx_copybutton adds a copy button to all code-blocks,
which improves useability of the documentation.

Thank you for contributing to the Bareos Project!

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.

Helpful documentation and best practices

• Git Workflow
• Automatic Sourcecode Formatting
• Check your commit messages

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

General

• PR name is meaningful
• Purpose of the PR is understood
• Separate commit for this PR in the CHANGELOG.md, PR number referenced is same
• Commit descriptions are understandable and well formatted

Source code quality

• Source code changes are understandable
• Variable and function names are meaningful
• Code comments are correct (logically and spelling)
• Required documentation changes are present and part of the PR
• check-sources --since-merge does not report any problems
• git status should not report modifications in the source tree after building and testing