Make file deletion on cache rebuild optional

Problem/Motivation

We consistently see Asset Injector file permission errors during cache rebuild ("The file permissions could not be set on public://asset_injector/..."). These are temporary but not fun on a production environment. The file deletion was added in #2869562: Deployment does not change asset files → for deployment purposes, but this isn't relevant to our workflow, we use config_ignore so that we can treat Asset Injector items as content instead of config. We'd like to be able to disable this file deletion on cache rebuild.

Proposed resolution

Add a parameter to make this functionality optional