Fix credential export and indentation in export, ReverseDSC improvements

[FabienTschanz]

Pull Request (PR) description

This PR fixes an issue where the Credential property in an export would be escaped and the indentation of an export is incorrect. It also adds the possibility to exclude the authentication properties from being updated as well as to allow variables in strings during final export conversion.

ATTENTION: Requires that microsoft/ReverseDSC#45 is merged first with an updated ReverseDSC version!

This Pull Request (PR) fixes the following issues

• Fixes The term '$Credscredential' is not recognized #5782

Task list

• Added an entry to the change log under the Unreleased section of the file CHANGELOG.md.
  Entry should say what was changed and how that affects users (if applicable), and
  reference the issue being resolved (if applicable).
• Resource parameter descriptions added/updated in the schema.mof.
• Resource documentation added/updated in README.md.
• Resource settings.json file contains all required permissions.
• Examples appropriately added/updated.
• Unit tests added/updated.
• New/changed code adheres to DSC Community Style Guidelines.

[FabienTschanz]

@NikCharlebois This PR and microsoft/ReverseDSC#45 belong together, and both are quite important for functionality to work properly. I found a couple of indentation issues and a nasty surprise with the Credential property in the resources that need to be resolved quickly so the customers don't generate invalid exports.

@ricmestre I believe all your issues should be addressed after this PR is merged.