cmd: add charon alpha add-validators-solo command

[xenowits]

Adds charon alpha add-validators-solo command to cmd package. It doesn't contain the actual functionality for adding validators.

category: feature
ticket: #1887

[codecov]

Codecov Report

Patch coverage: 38.59% and project coverage change: -0.09 ⚠️

Comparison is base (0f2b40f) 53.80% compared to head (801ca84) 53.71%.

❗ Current head 801ca84 differs from pull request most recent head 1f7841f. Consider uploading reports for the commit 1f7841f to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2280      +/-   ##
==========================================
- Coverage   53.80%   53.71%   -0.09%     
==========================================
  Files         188      190       +2     
  Lines       25542    25599      +57     
==========================================
+ Hits        13742    13750       +8     
- Misses      10113    10162      +49     
  Partials     1687     1687              

Impacted Files	Coverage Δ
cmd/alpha.go	0.00% <0.00%> (ø)
cmd/cmd.go	80.83% <0.00%> (-2.08%)	⬇️
cmd/addvalidators.go	50.00% <50.00%> (ø)

... and 12 files with indirect coverage changes

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