New ODCS release

• backend: Drop python 2 support
• backend: Remove non-latest symlink before creating
• cleanup: Delete unneeded requirement
• client: Add missing requirement openidc-client
• client: Customize user-agent of odcs-client
• client: Drop python 2 support
• client: improve create-tag --help description
• frontend: Allow ^ character in ODCS input.
• frontend: Allow querying rover groups
• frontend: Brand new API doc available at /api/1/
• frontend: Drop python 2 support
• frontend: Optimized metrics raw_config_types
• promote: Stop checking symlinks before promoting