feature: Support multiple index files with merging

[mrlunchbox777]

Contact Details

mrlunchbox777@gmail.com

Feature Description

Allow users to provide index file(s) that will be merged as union, support latest wins overwrites, on "name".

Why?

Allowing extra index files allows this to be customizable for tailoring for individual preference, and standardization for sharing and wide use.

What-should happen?

Users should be able to provide an array of directories that contain only overrides for the index file, with a default of an array with one item of <bbtctl resources dir>/index.d.

Covers this TODO.

Steps to Test

• Run the environment validation, it should only install defaults
• Run the environment validation with an index override in the default index.d dir, it should install the defaults in addition to what's in the file in the override dir
• Run the environment validation with an index override in the default index.d dir as well as one in a custom dir. Pass that custom dir to the packages overrides dirs, it should install the defaults in addition to what's in the file in the override dir and the custom dir

Code of Conduct

• [X] I agree to follow this project's Code of Conduct

[mrlunchbox777]

Should also cover this TODO.