Correctly evaluates the value of SITECORE_ENABLE_DEBUG

[pedrolamas]

Description

At the moment, setting the SITECORE_ENABLE_DEBUG environment variable to anything will enable debug, even if we set it to "false".

This ensures that we only enable debug if SITECORE_ENABLE_DEBUG is set to "true" (independently of case)

Motivation

Ensures that users can set SITECORE_ENABLE_DEBUG to "false" to disable SSR debug.

How Has This Been Tested?

In our local implementation

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• I have read the Contributing guide.
• My code follows the code style of this project.
• My change requires a change to the documentation.

[VaticanUK]

This seems a sensible change