Capture stderr in Git clone error

[rgmz]

Is your feature request related to a problem? Please describe.
When a clone fails, a vague error is printed to the console with the exit code. Unfortunately, 128 is a catch-all exit code for fatal events, so it isn't possible to determine the issue based on this alone.

For example, the following repository fails with exit status 128. However, in order to determine the actual cause we need to clone the repository ourselves:

# Poutine output
9:37PM | ERROR | failed to clone repo error="failed to clone repo: exit status 128" repo=ecomfe/stylecs

#  Git output
$ git clone https://github.com/ecomfe/es6-code-style
Cloning into 'es6-code-style'...
warning: You appear to have cloned an empty repository.

Describe the solution you'd like
Capture stderr in in the GitClient clone method.

poutine/providers/gitops/gitops.go

Line 50 in 4416b90

func (g *GitClient) Clone(ctx context.Context, clonePath string, url string, token string, ref string) error {

Describe alternatives you've considered
N/A

Additional context
N/A

[rgmz]

Incidentally, I think Clone can be simplified to the equivalent of:

$ git clone \
    --config "credential.helper=credentialHelperScript" \
    --config "submodule.recurse=false" \
    --depth=1 \
    --no-checkout \
    --no-tags \
    --sparse \
    --filter=blob:none  \
    <url>
# This assumes that workflows can only be under top-level `.github/`, which may not be correct.
$ git sparse-checkout set ".github/**/*.yml" ".github/**/*.yaml"
$ git checkout

In the latest version of Git, git sparse-checkout set automatically enables core.sparseCheckout and index.sparse.

poutine/providers/gitops/gitops.go

Lines 57 to 66 in 4416b90

	{"git", []string{"init", "--quiet"}},
	{"git", []string{"remote", "add", "origin", url}},
	{"git", []string{"config", "credential.helper", credentialHelperScript}},
	{"git", []string{"config", "submodule.recurse", "false"}},
	{"git", []string{"config", "core.sparseCheckout", "true"}},
	{"git", []string{"config", "index.sparse", "true"}},
	{"git", []string{"sparse-checkout", "init", "--sparse-index"}},
	{"git", []string{"sparse-checkout", "set", "**/*.yml", "**/*.yaml"}},
	{"git", []string{"fetch", "--quiet", "--no-tags", "--depth", "1", "--filter=blob:none", "origin", ref}},
	{"git", []string{"checkout", "--quiet", "-b", "target", "FETCH_HEAD"}},

[rgmz]

For example, the following repository fails with exit status 128. However, in order to determine the actual cause we need to clone the repository ourselves:

# Poutine output
9:37PM | ERROR | failed to clone repo error="failed to clone repo: exit status 128" repo=ecomfe/stylecs

#  Git output
$ git clone https://github.com/ecomfe/es6-code-style
Cloning into 'es6-code-style'...
warning: You appear to have cloned an empty repository.

With git clone --quiet, the only output is the error/warning.

$ git clone https://github.com/ecomfe/es6-code-style --quiet
warning: You appear to have cloned an empty repository.