Fixed header matching to be case insensitive

[marcinczeczko]

Description

The allowedRequestHeaders configurations that were using regexp to express which ones to allow where case sensitive. However, since the headers in HTTP are case insensitive we need to handle it the same way

Motivation and Context

Make header matching case insensitive

Screenshots (if appropriate):

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 not work as expected)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.

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