add querystring to force streaming on or off
add querystring to force streaming on or off

Test plan:
* on an endpoint that has streaming (like the modules index page)
* add a ?force_steam=1 to the url
* it should stream the page
* turn on enable_template_streaming in dynamic_settings.yml
* go to that same url, but without the query param
* it should still stream (as it did before)
* now add a ?force_stream=0 querystring to the url
* it should not stream the response

flag=none

Change-Id: I8d300f72e575771195198d21aa2b02a9a8337020
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/220439
Tested-by: Jenkins
Tested-by: Service Cloud Jenkins <9144042a601061f88f1e1d7a1753ea3e2972119d@instructure.com>
Reviewed-by: James Williams <3a5f4ed991dbfa5c9ef76ad729d240ca12f62180@instructure.com>
QA-Review: James Williams <3a5f4ed991dbfa5c9ef76ad729d240ca12f62180@instructure.com>
Product-Review: James Williams <3a5f4ed991dbfa5c9ef76ad729d240ca12f62180@instructure.com>

djbender/canvas-lms,instructure/canvas-lms,instructure/canvas-lms,djbender/canvas-lms,instructure/canvas-lms,instructure/canvas-lms,sfu/canvas-lms,djbender/canvas-lms,instructure/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,instructure/canvas-lms,sfu/canvas-lms,djbender/canvas-lms,sfu/canvas-lms,instructure/canvas-lms,sfu/canvas-lms,sfu/canvas-lms