Implement experimental REST API endpoints for plugins (#7279)

* Implement experimental REST API endpoints for plugins

* Updates per feedback and rebase

* Update tests

* Further updates

* Update extraction of plugins

* Use OS temp dir for plugins instead of search path

* Fail extraction on paths that attempt to traverse upward

* Update pluginenv ActivePlugins()

model/bundle_info.go

@@ -0,0 +1,20 @@
+package model
+
+type BundleInfo struct {
+	Path string
+
+	Manifest      *Manifest
+	ManifestPath  string
+	ManifestError error
+}
+
+// Returns bundle info for the given path. The return value is never nil.
+func BundleInfoForPath(path string) *BundleInfo {
+	m, mpath, err := FindManifest(path)
+	return &BundleInfo{
+		Path:          path,
+		Manifest:      m,
+		ManifestPath:  mpath,
+		ManifestError: err,
+	}
+}