Refactor directory structure: moving shared lib files to pkg

[yokawasa]

Description

Move the following shared libs to pkg from controllers

• cloudstorages/*.go
• notificationservices/*.go
• utils/*.go
• command.go + command_test.go

No additional code and no logic changed

This is a preparatory PR for supporting new providers (such as storages or notifications )

Test

• make test: OK
• CI / Test : OK
• manual integration test (not automated yet): OK

[yokawasa]

@taquaki-satwo @takuya-mikami @akitok thanks for the review !