feat: 💥 Allow creating multiple instances of app containers

[CLHatch]

Pull request

Purpose
Allow creating multiple instances of built-in apps without using an override.

Approach
Replace all references of the app's name in templates in .apps to $(appname} and ${APPNAME}.
On run, copy the folders of apps being used to .instances, using folder names similar to below.:

.instances/radarr
.instances/radarr__radarr4k

The "appname" variables in the files in these folders will be replaced by the folder name.

We will then use the .instances folder insstead of the .apps folders when creating the .env file.

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Learning
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Requirements
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