Plugin assets, external scripts and CSP overrides (#4260)

* Add assets for plugins
* Move plugin javascript and css into separate endpoints
* Allow loading external scripts
* Add csp overrides
* Only include enabled plugins
* Move URLMap to utils
* Use URLMap for assets
* Add documentation

internal/api/resolver_model_plugin.go

@@ -0,0 +1,57 @@
+package api
+
+import (
+	"context"
+
+	"github.com/stashapp/stash/pkg/plugin"
+)
+
+type pluginURLBuilder struct {
+	BaseURL string
+	Plugin  *plugin.Plugin
+}
+
+func (b pluginURLBuilder) javascript() []string {
+	ui := b.Plugin.UI
+	if len(ui.Javascript) == 0 && len(ui.ExternalScript) == 0 {
+		return nil
+	}
+
+	var ret []string
+
+	ret = append(ret, ui.ExternalScript...)
+	ret = append(ret, b.BaseURL+"/plugin/"+b.Plugin.ID+"/javascript")
+
+	return ret
+}
+
+func (b pluginURLBuilder) css() []string {
+	ui := b.Plugin.UI
+	if len(ui.CSS) == 0 && len(ui.ExternalCSS) == 0 {
+		return nil
+	}
+
+	var ret []string
+
+	ret = append(ret, b.Plugin.UI.ExternalCSS...)
+	ret = append(ret, b.BaseURL+"/plugin/"+b.Plugin.ID+"/css")
+	return ret
+}
+
+func (b *pluginURLBuilder) paths() *PluginPaths {
+	return &PluginPaths{
+		Javascript: b.javascript(),
+		CSS:        b.css(),
+	}
+}
+
+func (r *pluginResolver) Paths(ctx context.Context, obj *plugin.Plugin) (*PluginPaths, error) {
+	baseURL, _ := ctx.Value(BaseURLCtxKey).(string)
+
+	b := pluginURLBuilder{
+		BaseURL: baseURL,
+		Plugin:  obj,
+	}
+
+	return b.paths(), nil
+}