Fixes lazy load server protocols

[jasonb5]

Description

• Refactors CIME/Servers/__init__.py to use lazy loading via __getattr__ and @lru_cache
• No longer runs shutil.which() at import time for svn, wget, globus-url-copy
• Adds is_protocol_available(protocol) public API
• Updates check_input_data.py to use new API
• Adds 12 unit tests

Depends on: #4982

Checklist

• My code follows the style guidelines of this project (black formatting)
• I have performed a self-review of my own code
• My changes generate no new warnings
• I have added tests that exercise my feature/fix and existing tests continue to pass
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding additions and changes to the documentation

[github-actions]

You can preview documentation at https://esmci.github.io/cime/branch/fix/refactor-servers-lazyload/html/index.html