chia show keys --show-mnemonic-seed: Also show farmer private key

[xearl4]

Technically, the farmer process alone doesn't need the master secret key, but only the farmer secret key. This change therefore makes it easier to retrieve this derived secret key.

[xearl4]

Additional thoughts:

• We could show the pool secret key as well, if we think that helps OP plot farmers in some way.
• I'd like to harmonise naming between "master private key" and "wallet secret key" and use "secret key" everywhere. But I'm not sure what stability requirements you have on the CLI output.

[coveralls-official]

Pull Request Test Coverage Report for Build 6454238833

• 2 of 2 (100.0%) changed or added relevant lines in 1 file are covered.
• 106 unchanged lines in 11 files lost coverage.
• Overall coverage decreased (-0.1%) to 89.417%

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Files with Coverage Reduction	New Missed Lines	%
chia/wallet/util/wallet_sync_utils.py	1	77.21%
tests/simulation/test_simulation.py	1	96.53%
chia/server/node_discovery.py	2	77.49%
chia/timelord/timelord_api.py	2	87.85%
chia/full_node/full_node.py	3	85.5%
chia/server/server.py	4	79.54%
chia/full_node/full_node_api.py	7	77.68%
chia/daemon/server.py	8	86.19%
chia/wallet/wallet_node.py	9	87.03%
chia/timelord/timelord_state.py	20	69.47%

Totals
Change from base Build 6435114887:	-0.1%
Covered Lines:	87428
Relevant Lines:	97730

---

💛 - Coveralls

[github-actions]

This PR has been flagged as stale due to no activity for over 60 days. It will not be automatically closed, but it has been given a stale-pr label and should be manually reviewed by the relevant parties.

[paninaro]

@xchdata1 Thanks for the change. Would you be able to update the PR to target the release/2.1.2 branch?

The base branch was changed.

[xearl4]

@xchdata1 Thanks for the change. Would you be able to update the PR to target the release/2.1.2 branch?

Sure, done!