[rlp-v2] Do not use gateway name nor host in the RL domain

[guicassolato]

Currently the RLP controller fills the namespace^* attributes of the rate limit definitions, within a Limitador CR, with a string composed out of the Gateway namespaced name and hostname. Neither of those can be used to namespace the limits – and effectively the counters – or the following use cases cannot be addressed:

• HTTPRoute or Gateway lists multiple hostnames → one shared counter for the multiple hostnames
• HTTPRoute belongs to multiple Gateway parents → one shared counter for the multiple Gateway parents

^{* Named domain in the Envoy RateLimitRequest.}

A suggestion is to use the namespaced name of the RateLimitPolicy instead.

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Related to: Kuadrant/architecture#13, #156
Follows-up on: #199.