Add CertificateManager class

[josesimoes]

Description

• Add CertificateManager class.
• Add methods that allow adding/updating a CA Root certificate bundle to the device certificate store.
• ❗️❗️ Remove UpdateCertificates method from SslStream ❗️❗️ (and respective call in SslNative).

Motivation and Context

• The existing implementation lacks proper management of a X509 "certificate store". The only available method close to this was UpdateCertificates which was part of SslStream. Clearly not suitable for a regular use case where a certificate must exist on the SLL context prior to creating an SslStream and call any authenticate method.
• Addresses an issue and a kind-of design flaw inherited from .NETMF .

How Has This Been Tested?

• SSL sample from samples repo.

Screenshots

Types of changes

• Improvement (non-breaking change that improves a feature, code or algorithm)
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

Signed-off-by: José Simões jose.simoes@eclo.solutions