feature: allow using []string command instead of string

[rustatian]

Reason for This PR

ref: roadrunner-server/roadrunner#1667

Description of Changes

• Handle []string command case, when user can send raw command and avoid parsing by RR.

License Acceptance

By submitting this pull request, I confirm that my contribution is made under
the terms of the MIT license.

PR Checklist

[Author TODO: Meet these criteria.]
[Reviewer TODO: Verify that these criteria are met. Request changes if not]

• All commits in this PR are signed (git commit -s).
• The reason for this PR is clearly provided (issue no. or explanation).
• The description of changes is clear and encompassing.
• Any required documentation changes (code and docs) are included in this PR.
• Any user-facing changes are mentioned in CHANGELOG.md.
• All added/changed functionality is tested.

[codecov]

Codecov Report

Merging #85 (8062c2a) into master (16ad626) will decrease coverage by 0.03%.
The diff coverage is 66.66%.

@@            Coverage Diff             @@
##           master      #85      +/-   ##
==========================================
- Coverage   79.50%   79.47%   -0.03%     
==========================================
  Files          23       23              
  Lines        2000     2002       +2     
==========================================
+ Hits         1590     1591       +1     
- Misses        359      360       +1     
  Partials       51       51              

Files Changed	Coverage Δ
pool/config.go	100.00% <ø> (ø)
fsm/fsm.go	68.29% <50.00%> (-0.46%)	⬇️
pool/allocator.go	87.50% <100.00%> (ø)