feat(v4): Add API to fetch aggregate reports for inboxes (#10604)

The Inbox Overview section is being updated to offer a more detailed
report, showing an overall view of the account grouped by inboxes. To
view detailed reports and access specific graphs for individual inboxes,
click on the inbox name to navigate to its dedicated report page.

---------

Co-authored-by: Sojan Jose <sojan@pepalo.com>

app/builders/v2/reports/inbox_summary_builder.rb

@@ -0,0 +1,62 @@
+class V2::Reports::InboxSummaryBuilder < V2::Reports::BaseSummaryBuilder
+  pattr_initialize [:account!, :params!]
+
+  def build
+    load_data
+    prepare_report
+  end
+
+  private
+
+  attr_reader :conversations_count, :resolved_count,
+              :avg_resolution_time, :avg_first_response_time, :avg_reply_time
+
+  def load_data
+    @conversations_count = fetch_conversations_count
+    @resolved_count = fetch_resolved_count
+    @avg_resolution_time = fetch_average_time('conversation_resolved')
+    @avg_first_response_time = fetch_average_time('first_response')
+    @avg_reply_time = fetch_average_time('reply_time')
+  end
+
+  def fetch_conversations_count
+    account.conversations.where(created_at: range).group(group_by_key).count
+  end
+
+  def fetch_resolved_count
+    reporting_events.where(name: 'conversation_resolved').group(group_by_key).count
+  end
+
+  def fetch_average_time(event_name)
+    get_grouped_average(reporting_events.where(name: event_name))
+  end
+
+  def reporting_events
+    @reporting_events ||= account.reporting_events.where(created_at: range)
+  end
+
+  def prepare_report
+    account.inboxes.map do |inbox|
+      build_inbox_stats(inbox)
+    end
+  end
+
+  def build_inbox_stats(inbox)
+    {
+      id: inbox.id,
+      conversations_count: conversations_count[inbox.id] || 0,
+      resolved_conversations_count: resolved_count[inbox.id] || 0,
+      avg_resolution_time: avg_resolution_time[inbox.id],
+      avg_first_response_time: avg_first_response_time[inbox.id],
+      avg_reply_time: avg_reply_time[inbox.id]
+    }
+  end
+
+  def group_by_key
+    :inbox_id
+  end
+
+  def average_value_key
+    ActiveModel::Type::Boolean.new.cast(params[:business_hours]) ? :value_in_business_hours : :value
+  end
+end