feat(rpc); Add blockcommitments field to getblock output

[Metalcape]

Motivation

This PR adds the blockcommitments field to the getblock command output which is returned by zcashd and is required for FlyClient functionality.

Partially implements #9022 .

Solution

• Added a new commitment method to Header which returns the content of the commitment_bytes field in presentation byte order
• Added a block_commitments field to the response objects for both getblock and getblockheader
• Modified the get_block_header method of the RPC implementation to parse the value of the commitment_bytes field depending on the block's network and height

Tests

• Snapshots and tests were updated to take the new field into account.
• The value of the blockcommitments field was compared manually to the one returned by zcashd, before and after each network update.

Follow-up Work

To resolve #9022 we have to consider if the chainhistoryroot and authdataroot fields should also be added. The content of blockcommitments is equal to finalsaplingroot before Heartwood, and is equal to chainhistoryroot after Heartwood activation and before NU5.

PR Author's Checklist

• The PR name will make sense to users.
• The PR provides a CHANGELOG summary.
• The solution is tested.
• The documentation is up to date.
• The PR has a priority label.

PR Reviewer's Checklist

• The PR Author's checklist is complete.
• The PR resolves the issue.