[Staking ADO] Allow user to query current delegation info for defined validator

[crnbarr93]

Description

Upon staking a user should be able to query how much they have staked with a given validator and how much rewards they have accumulated.

Implementation

The query message for this is rather simple:

#[andr_query]
#[cw_serde]
pub enum QueryMsg {
  StakedTokens {
   #[returns(Option<Delegation>)]
    pub validator: Option<Addr>
  }
}

As for fetching staked tokens this can be done via this method. If no validator field is provided, use DEFAULT_VALIDATOR from state.

Acceptance Criteria

• A query to see delegations for a given validator
• Unit testing