Software SS: add CLI support for `self_service`

[mna]

#18834 (CLI part)

Checklist for submitter

• [x] Changes file added for user-visible changes in changes/, orbit/changes/ or ee/fleetd-chrome/changes. See Changes files for more information.
• [x] Input data is properly validated, SELECT * is avoided, SQL injection is prevented (using placeholders for values in statements)
• [x] Added/updated tests
• [x] Manual QA for all new/changed functionality

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

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Additional details and impacted files

@@                      Coverage Diff                      @@
##             feat-software-self-service   #19205   +/-   ##
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  Coverage                              ?   66.59%           
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  Files                                 ?      900           
  Lines                                 ?   111637           
  Branches                              ?        0           
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  Hits                                  ?    74348           
  Misses                                ?    31256           
  Partials                              ?     6033           

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backend	66.59% <100.00%> (?)

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[mna]

@roperzh I also thought it was going to be more involved tbh!