Python path setting (#2409)

* Add python package
* Add python path backend config
* Add python path to system settings page
* Apply python path to script scrapers and plugins

pkg/python/exec.go

@@ -0,0 +1,44 @@
+package python
+
+import (
+	"context"
+	"os/exec"
+
+	stashExec "github.com/stashapp/stash/pkg/exec"
+)
+
+type Python string
+
+func (p *Python) Command(ctx context.Context, args []string) *exec.Cmd {
+	return stashExec.CommandContext(ctx, string(*p), args...)
+}
+
+// New returns a new Python instance at the given path.
+func New(path string) *Python {
+	ret := Python(path)
+	return &ret
+}
+
+// Resolve tries to find the python executable in the system.
+// It first checks for python3, then python.
+// Returns nil and an exec.ErrNotFound error if not found.
+func Resolve() (*Python, error) {
+	_, err := exec.LookPath("python3")
+
+	if err != nil {
+		_, err = exec.LookPath("python")
+		if err != nil {
+			return nil, err
+		}
+		ret := Python("python")
+		return &ret, nil
+	}
+
+	ret := Python("python3")
+	return &ret, nil
+}
+
+// IsPythonCommand returns true if arg is "python" or "python3"
+func IsPythonCommand(arg string) bool {
+	return arg == "python" || arg == "python3"
+}