[MM-62066] Allow using plugin settings defined in manifest as fallback when using custom sections and plugin is disabled (#29500)

* Allow using plugin settings defined in manifest as fallback when using custom sections and plugin is disabled

* Update server/public/model/manifest.go

Co-authored-by: Christopher Poile <cpoile@gmail.com>

* Add custom setting case

---------

Co-authored-by: Christopher Poile <cpoile@gmail.com>
Co-authored-by: Mattermost Build <build@mattermost.com>

server/public/model/manifest.go

@@ -116,6 +116,9 @@ type PluginSettingsSection struct {
 
 	// If true, the section will load the custom component registered using `registry.registerAdminConsoleCustomSection`
 	Custom bool `json:"custom" yaml:"custom"`
+
+	// If true and Custom = true, the settings defined under this section will still render as fallback (unless the individual setting is type 'custom') when the plugin is disabled.
+	Fallback bool `json:"fallback" yaml:"fallback"`
 }
 
 type PluginSettingsSchema struct {

server/public/model/manifest_test.go

@@ -95,6 +95,18 @@ func TestIsValid(t *testing.T) {
 							},
 						},
 					},
+					{
+						Key:      "section3",
+						Custom:   true,
+						Fallback: true,
+						Settings: []*PluginSetting{
+							{
+								Key:         "section3setting1",
+								DisplayName: "thedisplayname",
+								Type:        "custom",
+							},
+						},
+					},
 				},
 			},
 		}, false},