Add cmd and endpoints to get validator delegations

[fedekunze]

Summary

Add new cmds and endpoints regarding delegations to a validator in order to provide an easy way to get insightful information and to avoid self DDoS.

Problem Definition

Currently the only way for a validator to get all the addresses that delegated to them is to do the following go through the staking transactions and filter them by their validator owner address and then get from each of them the address of the sender of the message.

Also, if they want to get delegation information they need to additionally query delegations one by one from delegator to validator, which might result in a self DDoS as previously seen in voyager/879.

This may require to add a new key for the KVStore.

Proposal

Implement the following queries in both CLI and Gaia-Lite:

• stake/validators/{validatorAddr}/delegators: Get all delegators that are bonded to a given validator
• stake/validators/{validatorAddr}/delegations: Get all delegations to a given validator

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[mslipper]

This appears to already be implemented in the CLI.

[rigelrozanski]

@mslipper I don't think this is implemented in either Rest or the CLI - you can get all the delegations from a delegator but not all delegations from different delegators to a single validator