openapi-request-validator: make mimetype header case insensitive

[pulasthieka]

HTML headers are lowercase most of the time, but some applications (eg:AWS) may use a different case. In such cases headers like content-type can be sent as Content-Type.

The request validator is written to throw an error when the request body is required AND content-type header is not present. Currently this error is thrown if content-type header is not in lowercase.

This fixes this issue and makes the content-type header case-insensitive

[pulasthieka]

Requested changes made

[jsdevel]

@pulasthieka please get the build to pass

[pulasthieka]

@pulasthieka please get the build to pass

Changes made to code formatting and now passes local workflow.

[pulasthieka]

@jsdevel can you trigger a PR build workflow