Simplify setup code for JS 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.

[aliu39]

From #14838 (comment)

We have to rethink this since we decided to prioritize global tracking. The user's setup code could still be simplified, but prioritizing other FF work for now

It's not ideal to pass in the global OpenFeature class or addHooks method. Having the user call addHooks seems fine for now.