tls-simple: fix client sample to trust the server CA and test the conn

[kevinawoo]

What was changed

• make the sample copy/paste-able
• trust the server public cert
• use client cert for auth
• test the connection by getting the version info

Why?

Make it easier to test this sample by having a easily copy/paste-able sample

Checklist

1. How was this tested: locally
2. Any docs updates needed? nope, we're good

[Copilot]

Pull Request Overview

This PR updates the tls-simple README example to be a copy/paste-able Go program that establishes a TLS/mTLS connection to Temporal and validates connectivity.

• Converts the snippet into a runnable main program.
• Trusts the server CA and supplies a client certificate for mTLS.
• Adds a connectivity check using GetSystemInfo.

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