Core - Client - Test Readme Issues

[faynef]

Section link1, link2:

Reason: link display error and extra characters.

Suggestion:

1. Add link for TestProxySanitizer: "https://github.com/Azure/azure-sdk-for-java/blob/main/sdk/core/azure-core-test/src/main/java/com/azure/core/test/models/TestProxySanitizer.java".
2. Add link for contributing guide: "https://github.com/Azure/azure-sdk-for-java/blob/main/CONTRIBUTING.md".
3. Add link for Microsoft Open Source Code of Conduct: "https://opensource.microsoft.com/codeofconduct/".
4. Add link for Code of Conduct FAQ: "https://opensource.microsoft.com/codeofconduct/faq/".
5. Remove the ..

@sandeep-sen , @joshfree and @alzimmermsft for notification.