[GOVCMSD8-282] Exclude node_modules from "ahoy lint"

[gargsuchi]

This PR does the following:

• Adds a lint-theme script to the code base - which excludes the path {PROFILE_DIR}/themes/custom/*/node_modules
• Adds phpcs.xml to the codebase
• Updates the Dockerfile.test to copy the above to the container
• Makes the lint-theme executable in the container

[tobybellwood]

Ah nice - so after this, we can remove the lint-theme steps from govcms/govcms8 and instead only have them here - given we don't expect a theme to be present at either govcms8 or govcms8lagoon. As I understand, it will just overwrite the existing file whilst it still exists.

[gargsuchi]

@tobybellwood That's correct.

[simesy]

Needs to go into here too. https://github.com/govCMS/scaffold-tooling/blob/develop/scripts/govcms-lint#L13