Simplify setup code for OpenFeatureIntegration

[aliu39]

Description

Like in python, we can call addHooks in the integration's setup method, optionally taking in an OpenFeature client. With this the user no longer has to call addHooks manually, and setup will match what we have for most integrations.

Current setup code

This shouldn't be done immediately since the integration was just released in 8.43. However it's still considered open beta, so this can be done before GA.

Pros:

• less setup code for users, less chance for error

Cons:

• inconsistent with LD setup code, where this separate call is necessary. This isn't much of a con IMO, because we expect providers to be different, it's more important to have JS and Python consistent.