[Release-1.28] Add ctr to shell completion

[vitorsavian]

• Issue -> [Release-1.28] - Add ctr to rke2 shell completion #6737
• Backport from -> Add ctr to shell completion #6709

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 13 lines in your changes missing coverage. Please review.

Project coverage is 25.11%. Comparing base (bc150d5) to head (bbcfa87).

Files with missing lines	Patch %	Lines
pkg/cli/cmds/completion.go	0.00%	13 Missing ⚠️

Additional details and impacted files

@@               Coverage Diff                @@
##           release-1.28    #6733      +/-   ##
================================================
- Coverage         25.18%   25.11%   -0.08%     
================================================
  Files                33       33              
  Lines              2831     2839       +8     
================================================
  Hits                713      713              
- Misses             2071     2079       +8     
  Partials             47       47              

Flag	Coverage Δ
inttests	9.54% <0.00%> (-0.03%)	⬇️
unittests	17.75% <0.00%> (-0.06%)	⬇️

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