Make 'new_window' a valid display type

[julianvu]

LTI tools registered using Dynamic Registration have no way of configuring navigation placements to open in a new tab instead of in frame. Adding 'new_window' to enum of VALID_DISPLAY_TYPES in InternalLtiConfiguration schema allows for this.

Test Plan:

• Configure an LTI 1.3 tool with the Course Navigation placement using Dynamic Registration, ensuring that the message object has the following:

"https://canvas.instructure.com/lti/display_type" : "new_window"

• Enable the tool in a course
• Select the course navigation link added by the tool. The tool should open in a new tab instead of in frame.

[julianvu]

The new_window display type is already supported internally to open LTI 1.3 tools in a new tab. The issue is new_window triggers a validation error if it's included in the tool registration request. Adding it to the enum will allow this parameter through, which will then allow a tool registered using Dynamic Registration to launch in a new tab.