[FSSDK-11635] remove duplicated fetch method, add cache wrapper

[Mat001]

• remove duplicated retry logic from cmab_service.go, only keep retry in cmab_client
• lru_cache file has been moved to own pkg.cache, that can break cache related to odp code, creating a cache wrapper such that all new code uses the new location in pkg/cache/cache.go and old odp code will stil be compatible and work with the old cache location.
• added deprecation comment to the wrapper

All unit tests pass, unchanged.

Jira: https://jira.sso.episerver.net/browse/FSSDK-11635