Record an informative stack trace & telemetry whenever `FilePath`...

Record an informative stack trace & telemetry whenever `FilePath` agent-to-controller access is permitted (#5890)

* Record an informative stack trace whenever `SlaveToMasterFileCallable` is permitted

* Also record telemetry as `SlaveToMasterFileCallableUsage`

* Deduplicate stack traces, and verify in test

* Push out end date to 2022-03-01

* `noopener noreferrer` needed on external links

Co-authored-by: Daniel Beck <1831569+daniel-beck@users.noreply.github.com>

* s/should/does/ in help

Co-authored-by: Daniel Beck <1831569+daniel-beck@users.noreply.github.com>

* Link to redirect w/ more info

Co-authored-by: Daniel Beck <1831569+daniel-beck@users.noreply.github.com>

* `mvn spotless:apply`

Co-authored-by: Daniel Beck <1831569+daniel-beck@users.noreply.github.com>
(cherry picked from commit 55c31c89)