Feature request: ag-project-files-regexp

[ghost]

On my machine, the output of ag --version is:

ag version 2.1.0

Features:
  +jit +lzma +zlib

My Emacs version is:

GNU Emacs 26.1 (build 1, x86_64-apple-darwin14.5.0, NS appkit-1348.17 Version 10.10.5 (Build 14F2511))
 of 2018-05-30

I'm using:

macOS 10.13.5

Feature request:

I would love an ag-project-files-regexp command which combines the functionality of ag-project-files with ag-project-regexp.

For example, I want to be able to search for a regular expression in all *.pl files in my project.