Feature/cleaner config install

[NoWiseMan]

Changelog: Feature: Skip "README.md" and "LICENSE.txt" during the installation of a custom config via conan config install.

Docs: conan-io/docs#1016

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This fixes #4258

The first line explains the changes

[CLAassistant]

All committers have signed the CLA.

[memsharded]

I am fine with this PR, it makes sense to skip those files.

Please add a note to the docs repo in a PR to develop branch.

One underlying issue is that conan-config-install works with multiple sources, but only caches and manages the last one. Some explicit representation of multiple conan-config-install sources might make sense, but that should be discussed separately.

Thanks for your contribution!

[NoWiseMan]

add PR to docs repro