feat!: Support transient identities and traits

[khvn26]

Closes #132.

[khvn26]

@gagantrivedi Keen to know if this approach is redundant. Maybe we could just go with a transient bool argument to respective interfaces.

[gagantrivedi]

Yeah, I'd prefer the latter approach

[khvn26]

Having implemented the bool argument, I don't quite like not being able to provide nil as the value. Since Golang doesn't support optional args, I feel we're forcing the majority of users to make the decision they don't need to make.

[gagantrivedi]

I think a bool pointer should be able to achieve that?

[khvn26]

It should, in theory, but then there's no way to provide a pointer to a constant (that I know of, at least).

[gagantrivedi]

Like this: https://github.com/open-feature/java-sdk?tab=readme-ov-file#targeting

[matthewelwell]

Hmm... yep, ok, that's a good point. Perhaps, for now, we should add that method and mark getEnvironmentFlags and getIdentityFlags as deprecated? To use transient identities, you will need to move to use the getFlags method.

[novakzaballa]

I also like implementing the OF interface with an evaluation context that can contain the identity. Actually, an immediate benefit of doing that is that we could optionally send the environment or another environment key in this call providing an easy way to "switch context" I guess, but that's just an example and another discussion.

[kyle-ssg]

Annoyingly I don't think it'll be as straight forward on the client-side with OF. In JS there's a single OF context. I wonder if this could be achieved using their concept of domains,

const domainScopedClient = OpenFeature.getClient("my-domain");
domainScopedClient.setContext(context1)

[khvn26]

@kyle-ssg Domain-specific contexts look like the exact solution for this.