Allow env show JSON with missing plugins

[xujiantop-crypto]

Closes #2011

Summary

• keep hatch env show --json usable when an environment type comes from a missing plugin
• preserve the raw environment config in the JSON output for unknown environment types
• add a regression test for JSON output with an unknown environment type

Tests

• python -m pytest tests/cli/env/test_show.py -q
• python -m pytest tests/cli/env/test_show.py::test_default_as_json_unknown_type tests/cli/env/test_show.py::test_default_as_json -q

[cjames23]

Your diff seems very odd for these changes.

[xujiantop-crypto]

Thanks for checking. I rechecked the branch locally against origin/master: the diff is only src/hatch/cli/env/show.py and tests/cli/env/test_show.py. If GitHub is showing a different compare view, I can rebase or recreate the branch.