feat:fountain:add grant-datacap support

[JesseXie]

Related Issues

adding the support to grant datacap from fountain

Proposed Changes

Add a new endpoint for grant datacap.

Additional Info

Checklist

Before you mark the PR ready for review, please make sure that:

• Commits have a clear commit message.
• [ x] PR title is in the form of of <PR type>: <area>: <change being made>
  • example: fix: mempool: Introduce a cache for valid signatures
  • PR type: fix, feat, build, chore, ci, docs, perf, refactor, revert, style, test
  • area, e.g. api, chain, state, market, mempool, multisig, networking, paych, proving, sealing, wallet, deps
• New features have usage guidelines and / or documentation updates in
  • Lotus Documentation
  • Discussion Tutorials
• Tests exist for new functionality or change in behavior
• CI is green

[maciejwitowski]

LGTM, thanks! (I'm not an expert in FIL+ though)

[arajasek]

I would consider sanity-checking that h.from is a valid verifier (notary) with enough data cap for this step, but that's optional.

For example of how to do so:

lotus/cli/filplus.go

Lines 656 to 676 in 6ca975e

	func checkNotary(ctx context.Context, api v0api.FullNode, vaddr address.Address) (bool, abi.StoragePower, error) {
	vid, err := api.StateLookupID(ctx, vaddr, types.EmptyTSK)
	if err != nil {
	return false, big.Zero(), err
	}
	act, err := api.StateGetActor(ctx, verifreg.Address, types.EmptyTSK)
	if err != nil {
	return false, big.Zero(), err
	}
	apibs := blockstore.NewAPIBlockstore(api)
	store := adt.WrapStore(ctx, cbor.NewCborStore(apibs))
	st, err := verifreg.Load(store, act)
	if err != nil {
	return false, big.Zero(), err
	}
	return st.VerifierDataCap(vid)
	}