Allow claiming staking rewards through smart contracts

[lumtis]

Describe the Issue
The staking precompile currently allow to manage stakes but not claiming rewards.

We should add the ability to claim the rewards to give full flexibility to build staking application (with the staking precompile the staker address might be a contract, currently this contract would not be able to stake the rewards)

Add the following methods:

// claim all staking rewards
claim() 

// fetch the current claimable rewards
// since we will allow ZRC20 rewards, could contains in argument what ZRC20 to fetch rewards, if null address or another boolean argument is specified, fetch native ZETA rewards
rewards() 

// (potentially)
// stake directly the rewards
stakeRewards()

Solution

Claiming is part of the distribution module and not staking module.

Two solutions:

• Extending staking precompile with the methods (preferred solution IMO)
• Implement the methods in a new or another precompile like distribution Add a precompile allowing to send ZRC20 to be distributed to stakers #2792

Other considerations

Some of the rewards would be in ZRC20 as Cosmos Coin version introduced in #2791

When claiming ZRC20., the ZRC20s should be directly sent to claimer as the ERC20 version, the users should never have to use the Cosmos native version.