Remove password parameter from X.509 constructors

[josesimoes]

Description

• Remove password parameter from X.509 constructors.
• Update code accordingly.
• Update comments and improve where needed.
• Bump AssemblyNativeVersion to 100.1.5.0
• Bump version to 1.9.0.

Motivation and Context

• MbedTLS is not able to decode X.509 certs with password. Only private keys. Same happens with Azure Netx Duo (our other secured network layer). So it doesn't make sense to keep offering a feature that we can't support.
• Despite being a breaking change (from the API perspective) it's not anticipated to cause any major hiccups in existing deployments as it is working as it is now (anyone trying to use it would have already complained about it by now).

How Has This Been Tested?

• TLS samples.

Screenshots

Types of changes

• Improvement (non-breaking change that improves a feature, code or algorithm)
• Bug fix (non-breaking change which fixes an issue with code or algorithm)
• New feature (non-breaking change which adds functionality to code)
• Breaking change (fix or feature that would cause existing functionality to change)
• Config and build (change in the configuration and build system, has no impact on code or features)
• Dependencies (update dependencies and changes associated, has no impact on code or features)
• Unit Tests (add new Unit Test(s) or improved existing one(s), has no impact on code or features)
• Documentation (changes or updates in the documentation, has no impact on code or features)

Checklist:

• My code follows the code style of this project (only if there are changes in source code).
• My changes require an update to the documentation (there are changes that require the docs website to be updated).
• I have updated the documentation accordingly (the changes require an update on the docs in this repo).
• I have read the CONTRIBUTING document.
• I have tested everything locally and all new and existing tests passed (only if there are changes in source code).
• I have added new tests to cover my changes.