Allow a module to specify if it does not want to make use of the update thread

[cubicgraphics]

No description provided.

[benaclejames]

We want to continue to encourage modules to utilize the update thread. This allows modlues to be better future-proofed in the case that it may become unsafe for two threads to write to UnifiedTrackingData at the same time, as well as allowing for VRCFT to better control each module's update threads for a cleaner de-init.

It's possible that in the future, managing the update loop will be optional and we'll just rely on different appdomains, but for now, we'd very much like to continue to incentivize developers to utilize this