Reenable SYSLIB0057 and fix the obsolete X509Certificate2 ctor usages

[akoeplinger]

In #56655 I had to disable the new SYSLIB0057 warning for the obsolete X509Certificate2 constructors (see dotnet/docs#41662 for details) to unblock the dependency flow.

These suppressions should be reverted and the obsolete usages replaced.

[mkArtakMSFT]

@akoeplinger do you plan to handle this and what timeline are you looking to tackle this in?

[akoeplinger]

I don't plan to handle this as I'm not familiar with the aspnetcore codebase, I just had to disable the warning to unblock codeflow.

[mkArtakMSFT]

@adityamandaleeka most of the code where the obsolete constructor is used is under your team's ownership. Leaving it up to you to prioritize and address.