Boilerplate TransactionFlinger

The short-term goal is to run locally and run both ad hoc and controlled
experiments for performance and correctness testing.

* bp and manifest boilerplate
* Activity to select a CUJ
* A trivial CUJ, just to have something to build more scaffolding around

Bug: 405591499
Flag: EXEMPT test only
Test: builds, installs, launch app
Change-Id: I8da84150b06473273d54608276b8c92e336cd862