Reward eligibility - specific keys

[cdummett]

To reward a set of users based off off-chain logic, add eligibility requirement, eligibile_keys - limits scopes of parties to those included in the set.

Doing:

• list of users in the recurring transfer

Not doing:

• maintain "team", whist is a list of users and specify the "team" id - unclear whether reusing team mechanics or new separate entity.

Use cases:

• focus testing on eligibile entities metric
• pro-rata
• ranked
• lottery
• w/ min position req
• w/ min staking req - for "staking rewards"

[davidsiska-vega]

For ACs needs to definitely work with:

• eligible entities metric
• eligible entities metric with lottery
• staking