Implement RFPs feature on contract

[PolyProgrammist]

RFP without RFP-proposals:

• [x] Create Timeline type for RFP [1h]
• [x] Add rules to manage RFPs' timeline [2h]
• [x] Create body for RFP (including it's timeline, submission deadline, subset of devhub proposal's fields) [3h]
• [x] Create all the methods for RFPs [8h]
• [x] Add a check that only admin can create RFP [1h]
• [x] Add a check that only admin can modify RFP [1h]
• [x] Add tests [4h]
• [x] Deploy on test contract [1h]
• [x] Create indices for RFPs [8h]
• [x] Provide examples on how to use the feature with near cli [3h]

Estimate: [32h] (27 april - 5 may)

RFP-proposals without RFPs:

• [x] Update body for RFP-proposal (including links to RFP and github project address) [2h]
• [x] Add tests [2h]
• [x] Deploy on test contract [1h]
• [x] Provide examples on how to use the feature with near cli [1h]
• [x] A method to add RFP link separately for a proposal [1h]
• [ ] Create opportunity to use labels as categories [3h]

Estimate: [7h] +? [5h] (6 May)

Connection between RFPs and RFP-proposals:

• [x] Add a check that if RFP is in evaluation and decision stage, no proposals are allowed to link and unlink to this RFP except admin [2h]
• [x] Add a check that at least one proposal should be approved for "Proposal Selected" stage [2h]
• [x] Don't allow to cancel RFP if there are active linked proposals [1h]
• [ ] Add RFP-proposal category auto update when RFP's category changes [1h]
• [x] Support devhub proposals migration from old contract [6h]
• [ ] Add tests [4h]
• [x] Deploy on test contract [1h]
• [ ] Create deployment action on Github [4h]
• [x] Test manually in production [4h]
• [ ] Add access control data including rules and moderators on test and in production [4h]
• [ ] Add categories data on test and in production [1h]
• [ ] Check that everything from infrastructure committee milestone is implemented [1h+]
• [ ] Complete Review [1-4 days including communication]
• [ ] Additional changes during frontend implementation and alpha testing [not included in this estimate]

Estimate: [31h] (7-13 May) + Review (1-4 days - up to 17 may) + Changes during frontend implementation & alpha testing