DEV: Add missing operationIds to the api docs (#14235)

From the openapi spec:

 https://spec.openapis.org/oas/latest.html#fixed-fields-7

each endpoint needs to have an `operationId`:

> Unique string used to identify the operation. The id MUST be unique
> among all operations described in the API. The operationId value is
> case-sensitive. Tools and libraries MAY use the operationId to uniquely
> identify an operation, therefore, it is RECOMMENDED to follow common
> programming naming conventions.

Running the linter on our openapi.json file with this command:

`npx @redocly/openapi-cli lint openapi.json`

produced the following warning on all of our endpoints:

> Operation object should contain `operationId` field

This commit resolves these warnings by adding an operationId field to
each endpoint.

spec/requests/api/notifications_spec.rb

@@ -15,6 +15,7 @@ describe 'notifications' do
 
     get 'Get the notifications that belong to the current user' do
       tags 'Notifications'
+      operationId 'getNotifications'
 
       produces 'application/json'
       response '200', 'notifications' do
@@ -60,6 +61,7 @@ describe 'notifications' do
 
     put 'Mark notifications as read' do
       tags 'Notifications'
+      operationId 'markNotificationsAsRead'
       consumes 'application/json'
       parameter name: :notification, in: :body, schema: {
         type: :object,