feat: handle other options for prefix

[cfabianski]

Description

Improve cases with a mix of prefixed and non-prefixed variable names

Details

We have this case https://github.com/Bearer/bearer/pull/1443/files#diff-327ba8d9bfe585949883f9a4e17edbdfec910d9bda37b0618a11a2e68e1cc1daR51-R69 where we want to have a mix of prefixed and non-prefixed environment variables.

We are passing an array EnvironmentVariables. We want to have a default behaviour (using AutomaticEnv(), SetEnvPrefix() and SetEnvKeyReplacer()) so that
scan.scanner would allow BEARER_SCANNER as well as BEARER_SCAN_SCANNER

But we also want to give it some more options where the prefix would be ignored like in the following
repository.url would allow BEARER_REPOSITORY_URL, ORIGIN_URL and CI_REPOSITORY_URL

Does that make sense?

[CLAassistant]

All committers have signed the CLA.

[github-actions]

👋 Thanks for contributing to Viper! You are awesome! 🎉

A maintainer will take a look at your pull request shortly. 👀

In the meantime: We are working on Viper v2 and we would love to hear your thoughts about what you like or don't like about Viper, so we can improve or fix those issues.

⏰ If you have a couple minutes, please take some time and share your thoughts: https://forms.gle/R6faU74qPRPAzchZ9

📣 If you've already given us your feedback, you can still help by spreading the news,
either by sharing the above link or telling people about this on Twitter:

https://twitter.com/sagikazarmark/status/1306904078967074816

Thank you! ❤️