Azure.Sdk.Tools.TestProxy_1.0.0-dev.20220107.1

Add header transform (#2485)

* Add header transform

* Fix test

* fix

* use original casing

* Docs

* Use conditions and unify sanitizers/transforms

* fix docs

* Fix

* Fix

* PR fb

* fix

* move validation

* Set header unconditionally in HeaderTransform

* docs

* more docs

* add more tests

* Fix condition