Add prep and storage rename CLI

[xinaxu]

This adds support for belwo commands

singularity prep rename old new
singularity storage rename old new

Also updated CONTRIBUTING.md for how to do this correctly as listed below

resolves #292

• Create a handler implementation under handler/* directory
• Make proper godoc comments for the implementation
• Add the handler function to the interface under handler/*/interface.go
• Update the MockHandler under handler/*/interface.go
• Create unit tests for this handler implementation
• Create a function to document the swagger API func _(){}
• Create corresponding API route handler in api/api.go
• Create a CLI command under cmd/* directory
• Update cmd/app.go to register the new command
• Add the CLI command unit test in one of cmd/*_test.go
• Optionally add CLI command integration tests in cmd/functional_test.go
• Run make generate or go generate ./...
• Add the swagger API unit test in api/api_test.go
• Optionally add swagger API integration tests in cmd/api_test.go

[codecov]

Codecov Report

Patch coverage: 68.42% and project coverage change: +3.49% 🎉

Comparison is base (72cbd09) 70.41% compared to head (1d875a5) 73.90%.
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #309      +/-   ##
==========================================
+ Coverage   70.41%   73.90%   +3.49%     
==========================================
  Files         130      134       +4     
  Lines        8065     8141      +76     
==========================================
+ Hits         5679     6017     +338     
+ Misses       1786     1488     -298     
- Partials      600      636      +36     

Files Changed	Coverage Δ
cmd/app.go	44.61% <ø> (ø)
cmd/storage/list.go	53.84% <ø> (ø)
docs/swagger/docs.go	100.00% <ø> (ø)
handler/dataprep/create.go	69.31% <ø> (ø)
handler/storage/create.go	94.54% <ø> (ø)
cmd/dataprep/rename.go	53.84% <53.84%> (ø)
cmd/storage/rename.go	53.84% <53.84%> (ø)
handler/dataprep/rename.go	71.42% <71.42%> (ø)
handler/storage/rename.go	71.42% <71.42%> (ø)
api/api.go	74.31% <100.00%> (+0.15%)	⬆️
... and 2 more

... and 9 files with indirect coverage changes

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[xinaxu]

@hannahhoward @elijaharita
See if above makes sense to you

[elijaharita]

i think it makes sense!