[HBAR Rate Limit Redesign] Add OPERATOR tier

[victor-yanev]

Instead of tracking the remaining total budget in-memory inside HbarLimitService (we would have to divide it by the number of Kubernetes instances, etc - it is creating unnecessary complexity in the configurations), we could create a new subscription tier (SubscriptionTier.OPERATOR) and add a pre-configured spending plan in the JSON configuration file which links the ETH address(es) of the relay operator account(s) to it.

In this way we can only set the total limit for the OPERATOR tier to HBAR_RATE_LIMIT_TINYBAR and it will be shared by all instances of the relay.