Support for reaching consensus on MintTx, mint client improvements

[eranrund]

Motivation

Similarly to #1630, we need to support submitting a MintTx to a consensus node, have it go through SCP, and end in the ledger together with TxOuts that are created as a result of the minting.
This PR provides that functionality.

In this PR

• Add a new GRPC endpoint to the consensus client service: ProposeMintTx.
• All the necessary plumbing to allow this new transaction type to go through SCP.
• Enclave modifications to allow including this transaction in a block, as well as for minting TxOuts.
• Improvements to the mc-consensus-mint-client utility.
• Changes to the local-network Python script so that it starts a v3 network with mintable tokens.

Future Work

• Lots and lots testing
• Improve the minting client to support offline flows and multiple MintConfigs when generating MintConfigTxs
• Altering the k8 setup to test this
• ... and more (ticketed in Asana)

Running locally

You will need to run the local network, see https://github.com/mobilecoinfoundation/mobilecoin/blob/master/tools/local-network/README.md for details on how to do that.
The local network script has been changed such that it has two mintable tokens, and the master minter keys are stored in /tmp/mc-local-network/minting-keys/master-minter1 (for token id 1) and /tmp/mc-local-network/minting-keys/master-minter2 (for token id 2).

Once the network is running, you need to propose a MintConfigTx in order to configure a minting configuration. For example, to do it for the 1st token: ./target/release/mc-consensus-mint-client generate-and-submit-mint-config-tx --node insecure-mc://localhost:3200/ --signing-key /tmp/mc-local-network/minting-keys/master-minter1 --token-id 1

The version of the minting client in this PR generates a single minting configuration, with a hardcoded amount (1000) and hardcoded signer key that is the same signing key that is used to sign the transaction. In real world, these keys would be different. That improvement would come in a future PR.

Once you successfully submitted a MintConfigTx, you should be able to mint to a b58 address of your choice: ./target/release/mc-consensus-mint-client generate-and-submit-mint-tx --node insecure-mc://localhost:3200/ --signing-key /tmp/mc-local-network/minting-keys/master-minter1 --recipient 8RwFxr8HXWDBozY7nqNcpuPFgj4o2XskkvnmT8gqSiN1jDUhLT5LpRK1M4aJ4huDvvkbby82rUeuRfCicVEKzYoqsbHkwcDHvE7AgxQ5aNM --token-id 1 --amount 1

To test that the minting worked, I used mobilecoind. The local network starts mobilecoind (on token id 0) and I ran another instance: ./target/release/mobilecoind --ledger-db /tmp/mc-local-network/mobilecoind-ledger-db1 --poll-interval 1 --mobilecoind-db /tmp/mc-local-network/mobilecoind-db1 --listen-uri insecure-mobilecoind://0.0.0.0:4445/ --watcher-db /tmp/mc-local-network/watcher-db1 --peer insecure-mc://localhost:3200/ --peer insecure-mc://localhost:3201/ --peer insecure-mc://localhost:3202/ --tx-source-url file:///tmp/mc-local-network/node-ledger-distribution-0 --tx-source-url file:///tmp/mc-local-network/node-ledger-distribution-1 --tx-source-url file:///tmp/mc-local-network/node-ledger-distribution-2 --token-id 1

I then used the mobilecoind python stuff to test this. I created a virtualenv (python3 -mvenv env), activated it (. ./env/bin/activate), installed the mobilecoin python lib (cd mobilecoind/clients/python/lib; python setup.py install) and then ran this script:

import mobilecoin

client1 = mobilecoin.Client('localhost:4444', False)
client2 = mobilecoin.Client('localhost:4445', False)

acct_key = client1.get_account_key(bytes([1] * 32)).account_key
monitor_id = client1.add_monitor(acct_key).monitor_id
pub_addr = client1.get_public_address(monitor_id).public_address
b58 = client1.create_address_code(pub_addr)
print(b58)

acct_key = client2.get_account_key(bytes([1] * 32)).account_key
monitor_id = client2.add_monitor(acct_key).monitor_id
pub_addr = client2.get_public_address(monitor_id).public_address
b58 = client2.create_address_code(pub_addr)
print(b58)

print('token id 0 balance', client1.get_balance(monitor_id))
print('token id 1 balance', client2.get_balance(monitor_id))

[eranrund]

This is an important change.

[remoun]

Optional/Equivalent: Borrow

Suggested change

	self.validate_mint_txs(&inputs.mint_txs)?;
	let mint_txs = inputs.mint_txs;
	let mint_txs = &inputs.mint_txs;
	self.validate_mint_txs(mint_txs)?;

[eranrund]

That wont work, since I am later moving it into BlockContents.

[remoun]

Nit: Add trailing newline