Configure file extensions for certificate authorities

[rjrudin]

Currently, DeployCertificateAuthoritiesCommand will only process filenames ending in ".crt". Should add a property - e.g. mlCertificateAuthorityFileExtensions - that allows for configuring what extensions to look for (it shouldn't blindly process every file since there could be a readme file in the directory with an extension that can't be predicted).

[rjrudin]

Documented at https://github.com/marklogic-community/ml-app-deployer/wiki/Certificate-Authorities

Ended up not adding a property but rather supporting a bunch of known certificate file extensions.