Add JSON response format to webhooks (#2671)

* Add JSON response format to webhooks

Support JSON responses for all webhook endpoints: index, show, create,
update, destroy, and activation. Adds jbuilder views, updates controllers
to use respond_to, and documents the API in docs/API.md.

* Address PR review feedback

- Use distinct board ID in API docs webhook example
- Use render "webhooks/show" in activations controller for consistency

* Address PR review feedback from flavorjones

- Include webhook.board in cache key to avoid stale board data
- Use _url instead of _path for location header consistency

* Fix webhook create test to match Location header format

Use board_webhook_url instead of board_webhook_path since the controller
returns a full URL in the Location header.

* Fix board ID in Location header example in API docs

Use distinct board ID in the Location URL to match the JSON body example.

app/controllers/webhooks_controller.rb

@@ -16,21 +16,45 @@ class WebhooksController < ApplicationController
   end
 
   def create
-    webhook = @board.webhooks.create!(webhook_params)
-    redirect_to webhook
+    @webhook = @board.webhooks.new(webhook_params)
+
+    if @webhook.save
+      respond_to do |format|
+        format.html { redirect_to @webhook }
+        format.json { render :show, status: :created, location: board_webhook_url(@webhook.board, @webhook, format: :json) }
+      end
+    else
+      respond_to do |format|
+        format.html { render :new, status: :unprocessable_entity }
+        format.json { render json: @webhook.errors, status: :unprocessable_entity }
+      end
+    end
   end
 
   def edit
   end
 
   def update
-    @webhook.update!(webhook_params.except(:url))
-    redirect_to @webhook
+    if @webhook.update(webhook_params.except(:url))
+      respond_to do |format|
+        format.html { redirect_to @webhook }
+        format.json { render :show }
+      end
+    else
+      respond_to do |format|
+        format.html { render :edit, status: :unprocessable_entity }
+        format.json { render json: @webhook.errors, status: :unprocessable_entity }
+      end
+    end
   end
 
   def destroy
     @webhook.destroy!
-    redirect_to board_webhooks_path
+
+    respond_to do |format|
+      format.html { redirect_to board_webhooks_path }
+      format.json { head :no_content }
+    end
   end
 
   private