feat: make suites mandatory in archive config

[HadrienPatte]

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This PR makes the suites attribute of archives in the chisel.yaml mandatory. All other attributes are already mandatory (version, components and keys).
There was an old fallback logic which would set suites to the release adjective if left unset, but this logic was only configured for 4 ubuntu releases, one of which (bionic) is no longer supported by chisel, and all other three have their suites properly configured in their chisel.yaml already, so this piece of logic never triggers (focal, jammy, kinetic).

[rebornplusplus]

Thanks for the PR!

Please note that some other packages (main and slicer) have tests without the archives.<archive>.suites field. We need to update those too.

I can't trigger the CI, but the unit tests are failing actually (ran locally):

$ go test ./... -count=
1
?       github.com/canonical/chisel/cmd [no test files]
?       github.com/canonical/chisel/internal/archive/testarchive        [no test files]

----------------------------------------------------------------------
FAIL: cmd_info_test.go:209: ChiselSuite.TestInfoCommand

Summary: A single slice inspection
cmd_info_test.go:230:
    c.Assert(err, IsNil)
... value *errors.errorString = &errors.errorString{s:"chisel.yaml: archive \"ubuntu\" missing suites field"} ("chisel.yaml: archive \"ubuntu\" missing suites field")

OOPS: 2 passed, 1 FAILED
--- FAIL: Test (0.01s)
FAIL
FAIL    github.com/canonical/chisel/cmd/chisel  0.028s
ok      github.com/canonical/chisel/internal/archive    0.193s
ok      github.com/canonical/chisel/internal/cache      0.014s
ok      github.com/canonical/chisel/internal/control    0.006s
?       github.com/canonical/chisel/internal/deb/chrorder       [no test files]
ok      github.com/canonical/chisel/internal/deb        0.067s
ok      github.com/canonical/chisel/internal/fsutil     0.033s
ok      github.com/canonical/chisel/internal/jsonwall   0.007s
ok      github.com/canonical/chisel/internal/manifest   0.013s
ok      github.com/canonical/chisel/internal/pgputil    0.024s
ok      github.com/canonical/chisel/internal/scripts    0.041s
ok      github.com/canonical/chisel/internal/setup      17.924s

----------------------------------------------------------------------
FAIL: slicer_test.go:1090: S.TestRun

Summary: Basic slicing
slicer_test.go:1092:
    // Run tests for format chisel-v1.
    runSlicerTests(c, slicerTests)
slicer_test.go:1136:
    c.Assert(err, IsNil)
... value *errors.errorString = &errors.errorString{s:"chisel.yaml: archive \"ubuntu\" missing suites field"} ("chisel.yaml: archive \"ubuntu\" missing suites field")

OOPS: 2 passed, 1 FAILED
--- FAIL: Test (0.01s)
FAIL
FAIL    github.com/canonical/chisel/internal/slicer     0.100s
ok      github.com/canonical/chisel/internal/strdist    0.007s
ok      github.com/canonical/chisel/internal/testutil   12.272s
FAIL

[letFunny]

Looks good to me. We need to discuss if we want to remove the defaults or configure them properly, probably the former.

[rebornplusplus]

Looks good to me, thank you!

[niemeyer]

This looks reasonable, thanks for the suggestion. We need to discuss the possible removal of the version field as well, which was used for assuming details before. But we'll do it separately.