Add validation on rate-limit ingress annotations

[vepatel]

Similar to rate-limit policies in VS/VSR, below annotations should be mandatory i.e. at least these 3 annotations should be present in Ingress if a user wishes to configure rate-limiting:

    nginx.org/limit-req-rate: 1r/s
    nginx.org/limit-req-key: ${binary_remote_addr}
    nginx.org/limit-req-zone-size: 10M

[github-actions[bot]]

Hi @vepatel thanks for reporting!

Be sure to check out the docs and the Contributing Guidelines while you wait for a human to take a look at this :slightly_smiling_face:

Cheers!