feat: support custom minimum voting power score when voting on offchain proposals

[wa0x6e]

Currently, we only check that the user's voting power is > 0 to allow voting on offchain spaces.

We should retrieve the minScore from the voteValidation property on offchain proposal, and set the minimum score for voting from it (onchain proposals will always have minScore = 0)

This score will be used in the votingPower composable/stores to determine whether a user can vote on a proposal, or create a space, and show the corresponding warning message

This feature will be based on #511 (extracted as the vote reason PR is heavy enough, and not restart the review process)