New Feature - When creating the allocation requests, check if the issue has a pending proposal

[fabriziogianni7]

Description

When creating the allocation requests, check if the issue has a pending proposal. if it has, we should:

1. copypaste the proposal instead of creating a new request
2. change the labels accordingly to match the proposed status

Context

This feature is needed because sometimes we can have multiple pending proposals like in this case --> filecoin-project/filecoin-plus-large-datasets#326

it happened that 2 notaries proposed the datacap allocation.
when a notary comes to approve this, he will sign one of the 2 approvals, leaving the other in pending state.
without this change, the bot will propose a new datacap allocation and when a notary will sign the proposals, he will create another transactionID.
We want to avoid this. How?
By retrieving the pending proposal from the issue and repasting it in it, adjusting the labels.
This way, in the app dashboard, this issue will appear having one proposal.

Challenge:

get the right proposal to repost.