Validate the launch closer to the actual launch

[jonespm]

I believe some issues with launch validation might be because we are waiting a bit to do any launch validation.

If we explicitly validate the launch immediately after the launch we shouldn't encounter issues with the validation not matching, and if so be able to handle it better in our code.

https://github.com/dmitry-viskov/pylti1.3#lti-message-launches

I'm not sure if we'd need to implement any locking around this. We're doing more testing. I believe that if the testing is successful just having a validate closer to the launch should be sufficient.

canvas-app-explorer/backend/canvas_app_explorer/lti1p3.py

Line 182 in a7a8f86

message_launch = ExtendedDjangoMessageLaunch(request, TOOL_CONF, launch_data_storage=CacheConfig.launch_data_storage)