Add missing methods to ClientInterface.php

[jmrieger]

PHP SDK

What did you accomplish?

• Update ClientInterface to add missing public methods that were available on Client and LocalhostClient

How do we test the changes introduced in this PR?

• Existing unit tests and regression should be sufficient.
• Consumers of the library should now be able to freely use ClientInterface in place of the concrete implementation's FQCN.

Extra Notes

n/a

[jmrieger]

Unrelated to this specific change, composer.json is currently set up to require rmccue/requests, but I can't find a place that it's actually used in the production portion of this library. It looks like it was in use at some point in bin/splitio before the Split Synchronizer became a product.

If that package isn't needed, can it be removed, or at a minimum moved to require-dev? I can include it as part of this PR, or as a separate piece.

[mredolatti]

Hi @jmrieger, thank you very much for this contribution. We will send this to our staging environment, and let you know when it's released. As for the extra library. It's true that it's no longer used since the PHP synchronizer is deprecated. A code & library cleanup is in order, and hopefully should make it to the next release.

Once again thank you very much for reaching out.
Martin.