RTECO-1564 - Add Apt to ProjectTypes and ProjectType constants

[fluxxBot]

• All tests passed. If this feature is not already covered by the tests, I added new tests.
• All static analysis checks passed.
• This pull request is on the master branch.
• I used gofmt for formatting the code before submitting the pull request.

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Summary

• Add Apt ProjectType constant to the ProjectType iota in common/project/projectconfig.go
• Add "apt" string to ProjectTypes slice at the matching index

Why

jf setup and jf setup apt need to route the apt package manager through the
same SetupCommand framework used by npm, go, pip, etc. — for interactive repo
selection (promptUserToSelectRepository) and for listing apt in
GetSupportedPackageManagersList(). Both rely on a ProjectType value existing
for apt.

Without this change the string "apt" has no enum counterpart, so the setup
framework cannot filter debian repositories or dispatch to configureApt().