Enhancement - Option to parameterize transaction controller

**Ankush Garg** ([Bug 63127](https://bz.apache.org/bugzilla//show_bug.cgi?id=63127&redirect=false)):
We are trying to achieve something like:

1) Use selenium to navigate web application and Jmeter to capture network traffic.
2) Would like to combine requests based on business case using Transaction controller. for e.g. - Requests could be combined in transactions Login, Add items to cart, Checkout, Payment.
3) Transactions created in Step 2 helps in combining response times of multiple requests.
4) Don't want to add transaction controller manually.
5) APIs can be exposed using which transaction controller can be added and start/pause/stop recording from java code and not from UI. Users can override it via plugin.

OS: All