Support for readonly (RO) georadius commands

[ursNiemi]

Currently it is not possible to use readonly variants GEORADIUS_RO and GEORADIUSBYMEMBER_RO. Please add these readonly variants.

See:

• Discussion: https://github.com/redis/redis/issues/4084
• Commit: https://github.com/redis/redis/commit/d557144ebbd58deb67cfbddf4d5c675bafb523c6
• Documentation: https://redis.io/commands/georadius

[arjunmehta]

@ursNiemi Welcome any PRs that would help implement this