API: Add participation key generation endpoint to algod API

[winder]

Summary

Implementation for #5578.

New endpoint for the admin API to generate and install participation keys.

POST /v2/participation/generate/{address}

The participation keys are generated in the background and installed when generation is complete. With this PR there is no progress reporting. Programs should poll the GET /v2/participation endpoint and look for the new key to appear. Once the new key is installed a key registration transaction can be made.

Test Plan

New unit tests.

[codecov]

Codecov Report

Merging #5781 (ecc16b0) into master (d3df476) will increase coverage by 0.00%.
The diff coverage is 38.27%.

@@           Coverage Diff           @@
##           master    #5781   +/-   ##
=======================================
  Coverage   55.53%   55.53%           
=======================================
  Files         473      474    +1     
  Lines       66815    66851   +36     
=======================================
+ Hits        37105    37127   +22     
- Misses      27192    27199    +7     
- Partials     2518     2525    +7     

Files	Coverage Δ
daemon/algod/api/server/v2/test/helpers.go	77.15% <100.00%> (+0.11%)	⬆️
data/account/participation.go	63.97% <100.00%> (+0.53%)	⬆️
cmd/goal/account.go	13.61% <0.00%> (-0.06%)	⬇️
daemon/algod/api/server/router.go	16.00% <0.00%> (-0.33%)	⬇️
libgoal/participation.go	0.00% <0.00%> (ø)
libgoal/participation/participation.go	66.66% <66.66%> (ø)
daemon/algod/api/server/v2/handlers.go	0.77% <0.00%> (-0.02%)	⬇️

... and 12 files with indirect coverage changes

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[jannotti]

I had some comments that I forgot to submit. I think I still have more to look at and understand though.

[jannotti]

I left some very small nits, but approving. If you want to change them, I'll reapprove immediately. Up to you.

[ohill]

LGTM