[DotNet] Add details to README in certificate samples

[JhontSouth]

#minor

Description

This PR adds more information to the README certificate samples to have an easier complete guide for SSL/TLS certificate configuration.

Proposed Changes

• Updated Readme of dotnet samples 84.bot-authentication-certificate and 85.bot-authentication-sni.

[JhontSouth]

Include az login step

[sw-joelmut]

I created #429 to improve the readme, and merge it to this pr once approved

For SNI it also applies the same principles

[sw-joelmut]

We should replace this https://github.com/southworks/BotBuilder-Samples/pull/421/files#diff-7dbeff6709649d9c6e9229f72bcdc4d92ab7e4b89670961266729f98010d7769R55-R58 with the CertificateServiceClientCredentialsFactory like the normal certificate sample, but sendX5c.

[JhontSouth]

We should replace this https://github.com/southworks/BotBuilder-Samples/pull/421/files#diff-7dbeff6709649d9c6e9229f72bcdc4d92ab7e4b89670961266729f98010d7769R55-R58 with the CertificateServiceClientCredentialsFactory like the normal certificate sample, but sendX5c.

I guess that you are referring to this(the link doesn't work):
services.AddSingleton(
new CertificateServiceClientCredentialsFactory(certificate, _configuration["MicrosoftAppId"], _configuration["MicrosoftAppTenantId"], null, null, true));

Instead of:

        // MSAL certificate auth.
        services.AddSingleton(
            serviceProvider => ConfidentialClientApplicationBuilder.Create(_configuration["MicrosoftAppId"])
                .WithCertificate(certificate, sendX5C)
                .Build());

        // MSAL credential factory: regardless of secret, cert or custom auth, need to add the line below to enable MSAL.
        services.AddSingleton<ServiceClientCredentialsFactory, MsalServiceClientCredentialsFactory>();

[sw-joelmut]

Yes, also the image in the readme should be updated.

[JhontSouth]

services.AddSingleton(
new CertificateServiceClientCredentialsFactory(certificate, _configuration["MicrosoftAppId"], _configuration["MicrosoftAppTenantId"], null, null, true));

solved

[JhontSouth]

Promoted /3995