Add information about the new lock-env and lock-config options

[avstudnitz]

…for bin/magento config:set

This PR is a:

[ ] New topic
[X] Content fix or rewrite
[ ] Bug fix or improvement

Summary

When this pull request is merged, it will add information about the new lock-env and lock-config options for bin/magento config:set, how to use them and when.

Additional information

You can find more information about that topic at https://www.integer-net.com/magento-2-2-configuration-via-code/.

whatsnew
Added descriptions for the new magento config:set lock-env and lock-config options.

[magento-cicd2]

All committers have signed the CLA.

[keharper]

@avstudnitz Thank you for your code and documentation contributions.

A couple of questions before I start processing your pull request.

• Has this feature been accepted for 2.3?
• Are fields that were previously locked affected in any way?

I might need to restructure the topic to make it easier for users to find pre-2.2.4 and 2.2.4+ information, but I haven't gone through the details yet.

[keharper]

@avstudnitz Another question: Can you specify --lock-config and --lock-env in the same command?