Populate BlockTemplate fields using a new state request

[oxarbitrage]

Motivation

Whatever is not fixed values(#5452), coinbase transaction(#5453) or mempool transaction(#5454) will be state or Rust API values.

Tasks

Return state values in the getblocktemplate RPC method response:

• previousblockhash
• height
• defaultroots
  • chainhistoryroot
• target (same as bits, but in a different format)
• mintime

These values should come from a new state request based on recent best blocks. We want to use a single state request for performance.

Return local node clock value in the getblocktemplate RPC method response:

• curtime - using the same standard library time function as the time field consensus rule check

Related Tickets

Depend on #5451
Can depend on #5452 for identification

[teor2345]

@oxarbitrage I think the fields we need here are:

New state request based on recent best blocks:

• previousblockhash
• height
• defaultroots
  • chainhistoryroot
• target (same as bits, but in a different format)
• mintime

Standard library time function:

• curtime

Can I edit the ticket, or did you want to?

[oxarbitrage]

Please feel free to edit any of the getblocktemplate tickets. I did some some work already in the first one but none in the rest of them.

[mpguerra]

Hey team! Please add your planning poker estimate with Zenhub @arya2 @conradoplg @dconnolly @oxarbitrage @teor2345 @upbqdn

[teor2345]

PR #5659 populates all of these fields except defaultroots.chainhistoryroot (and the 5 fields that are copies of it).

@mpguerra @oxarbitrage did you want to split that out into a separate ticket?

[mpguerra]

I think @oxarbitrage is working on them in a separate PR so I think it's ok to just keep it in this ticket.