feat: Added Instagram channel migration (#11181)

This PR is part of https://github.com/chatwoot/chatwoot/pull/11054 to
make the review cycle easier.

spec/models/channel/instagram_spec.rb

@@ -0,0 +1,17 @@
+# frozen_string_literal: true
+
+require 'rails_helper'
+
+RSpec.describe Channel::Instagram do
+  let(:channel) { create(:channel_instagram) }
+
+  it { is_expected.to validate_presence_of(:account_id) }
+  it { is_expected.to validate_presence_of(:access_token) }
+  it { is_expected.to validate_presence_of(:instagram_id) }
+  it { is_expected.to belong_to(:account) }
+  it { is_expected.to have_one(:inbox).dependent(:destroy_async) }
+
+  it 'has a valid name' do
+    expect(channel.name).to eq('Instagram')
+  end
+end