✨ allow probes to collect their own data from repo clients

[spencerschrock]

What kind of change does this PR introduce?

feature

• PR title follows the guidelines defined in our pull request documentation

What is the current behavior?

probes must have the data they rely on in some check's raw result

What is the new behavior (if this is a feature change)?**

• introduce "independent" probes which fetch data directly from the repo client
• Allow these probes to run when specified via --probe
  • since this is only for probes which don't belong to checks, the logic around running probes from the various check/*.go functions doesn't need modified

• Tests for the changes have been added (for bug fixes/features)

Which issue(s) this PR fixes

Fixes #3235

Special notes for your reviewer

Does this PR introduce a user-facing change?

For user-facing changes, please add a concise, human-readable release note to
the release-note

(In particular, describe what changes users might need to make in their
application as a result of this pull request.)

NONE

[spencerschrock]

You can see an example of a toy probe which does its own data collection here.

func init() {
	probes.MustRegisterIndependent(Probe, Run)
}

//go:embed *.yml
var fs embed.FS

const Probe = "foo"

func Run(cr *checker.CheckRequest) ([]finding.Finding, string, error) {
	if cr == nil {
		return nil, "", fmt.Errorf("%w: check request", uerror.ErrNil)
	}

	name, err := cr.RepoClient.GetDefaultBranchName()
	if err != nil {
		return nil, Probe, fmt.Errorf("fetching default branch name: %w", err)
	}

	// ...
}

Which works as expected:

go run main.go --repo ossf/scorecard --probes foo --format probe | jq
{
  "date": "2024-04-24",
  "repo": {
    "name": "github.com/ossf/scorecard",
    "commit": "43022835f28208561e72b9ffbdc95aa8dfc35421"
  },
  "scorecard": {
    "version": "devel",
    "commit": "unknown"
  },
  "findings": [
    {
      "remediation": {
        "text": "foo?",
        "markdown": "",
        "effort": 1
      },
      "probe": "foo",
      "message": "not foo!!",
      "outcome": "False"
    }
  ]
}