feat: Support reading default init sources from ~/.hermit.hcl

[lox]

This PR introduces a new init_sources field to the Hermit user configuration file (~/.hermit.hcl). This field allows users to specify a default set of sources to be used when initializing a new Hermit environment with the hermit init command.

Example ~/.hermit.hcl:

init_sources = [
  "https://github.com/lox/private-hermit-packages.git", 
  "https://github.com/cashapp/hermit-packages.git"
]

This means any call to hermit init will use these sources.

[lox]

I'm testing it with:

rm -rf ~/test-hermit; mkdir ~/test-hermit; go run ./cmd/hermit -t init ~/test-hermit

I see the sources added correctly to ~/test-hermit/bin/hermit.hcl.

I couldn't see any existing tests for the area, any suggestions there?

[nickajacks1]

I couldn't see any existing tests for the area, any suggestions there?

Perhaps it makes sense to add tests in it/full?
LoadUserConfig would probably need to be updated to be able to load from a custom path though.

[lox]

I can't seem to get rid of this log line:

2025/02/12 15:29:58 ~/.hermit.hcl: 2:1: found extra fields "init_sources"

[lox]

@nickajacks1 tests added!

[nickajacks1]

@lox I got some failed tests when running the full test, can you check that?
Example

  34) Hermit Isolated Runtime dependencies can call isolatedenv2 binary from testenv
      When call ./bin/isolatedenv2

      34.1) The stderr should be blank

              expected: blank (unset or zero length string)
                   got: "userConfigPath:
              2025/02/16 18:07:47 : read /home/njackson/source/hermit/it/full/testenv: is a directory
              userConfigPath:
              2025/02/16 18:07:47 : read /home/njackson/source/hermit/it/full/testenv: is a directory
              userConfigPath:
              2025/02/16 18:07:48 : read /home/njackson/source/hermit/it/full/testenv: is a directory"

            # spec/it_spec.sh:439

[alecthomas]

Maybe you want github-token-auth to be read from there as well?

[lox]

Yup, absolutely, was going to do that in another PR unless you want it here @alecthomas