Adjust prettier configuration to respect config files if they already exist

Migrated issue

Reported by: hestenet

Related to !15 (merged)

Problem/Motivation

This is a follow-up from #3357971: ESLINT needs the eslint-plugin-prettier plugin and the comments on gitlab_templates/-/merge_requests/14

@jonathan1055
These link statements need to check if the file already exists. Contrib can have either of these files, and if they exist (a) the existing file should be left intact, and (b) the ln command fails anyway.

@jonathan1055
I fixed this in my override version using

    - if [[ ! -f .prettierrc.json ]] ; then ln -s $_WEB_ROOT/core/.prettierrc.json . ; fi
    - if [[ ! -f .prettierignore ]]; then ln -s $_WEB_ROOT/core/.prettierignore .; fi

Proposed resolution

TBD

Remaining tasks

TBD