Add Xdebug

Closes #5

See merge request !25

Adding to the PHP images because certain WP-specific Grunt tasks rely on PHP,
so it makes sense to have it all in one place.

See also gitlab/ci/wordpress#1

Adding to the PHP images because certain WP-specific Grunt tasks rely on PHP,
so it makes sense to have it all in one place.

See also gitlab/ci/wordpress#1

Adding to the PHP images because certain WP-specific Grunt tasks rely on PHP,
so it makes sense to have it all in one place.

See also gitlab/ci/wordpress#1

Adding to the PHP images because certain WP-specific Grunt tasks rely on PHP,
so it makes sense to have it all in one place.

See also gitlab/ci/wordpress#1

Add project-agnostic dependency to Golang image

See merge request !24

Each project needn't install this dependency during CI setup

Add PHP 8.1

See merge request !23

Add image for Debian Bullseye

See merge request !21

Remove disused PHP 5.3 image

See merge request !20

Bump WP Deploy container to latest

See merge request !19

Add images for PHP 7.4 and 8.0

See merge request !18

Update Golang image for Buster

See merge request !17

Add dependencies for building Debian packages

See merge request !16

Restore WP.org plugin image as a submodule

See merge request !15

Remove WP.org plugin-deploy image

See merge request !14