feat: add genesis validator subcommand

[zivkovicmilos]

Description

This PR adds support for the genesis validator sub-commands, as outlined in #1228.

Closes #1228

Example genesis validator add command you can use to test out the functionality:

genesis validator add --name milos -pub-key gpub1pgfj7ard9eg82cjtv4u4xetrwqer2dntxyfzxz3pqvknvnspy43c9zp0ts7wgvupldfzkws8kmvvz2eelfmzzupfymwpwzhh9m3 -address g1wpewvuxtyvqqwysndt4f8425tpdg3lf0mhu6fm

Contributors' checklist...

• Added new tests, or not needed, or not feasible
• Provided an example (e.g. screenshot) to aid review or the PR is self-explanatory
• Updated the official documentation or not needed
• No breaking changes were made, or a BREAKING CHANGE: xxx message was included in the description
• Added references to related issues and PRs
• Provided any useful hints for running manual tests
• Added new benchmarks to generated graphs, if any. More info here.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (69a1714) 47.27% compared to head (507143d) 47.77%.

Additional details and impacted files

@@               Coverage Diff                @@
##           feat/genesis    #1259      +/-   ##
================================================
+ Coverage         47.27%   47.77%   +0.49%     
================================================
  Files               367      369       +2     
  Lines             61467    62656    +1189     
================================================
+ Hits              29059    29934     +875     
- Misses            30029    30289     +260     
- Partials           2379     2433      +54     

Files	Coverage Δ
tm2/pkg/crypto/keys/client/add.go	31.05% <ø> (-0.32%)	⬇️
tm2/pkg/crypto/keys/client/helper.go	50.00% <ø> (-7.15%)	⬇️

... and 9 files with indirect coverage changes

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[gfanton]

lgtm