Fix #635: Support specifying alternative provider TLS trust source(s) (#645)

* Fix #635: Support specifying alternative provider TLS trust source(s)

* Update pkg/apis/options/options.go

Co-authored-by: Joel Speed <Joel.speed@hotmail.co.uk>

* Update pkg/validation/options.go

Co-authored-by: Joel Speed <Joel.speed@hotmail.co.uk>

* Address review comments

* upd CHANGELOG.md

* refactor test to assert textual subjects + add openssl gen cmd

Co-authored-by: Joel Speed <Joel.speed@hotmail.co.uk>