Support fallback for hasFeature, add options.skipAnalytics

[rolodato]

This change solves https://github.com/Flagsmith/flagsmith-js-client/issues/243 by adding a fallback option to hasFeature, instead of changing how defaultFlags works. It also deprecates the current way of using skipAnalytics but preserves backwards compatibility.

I chose to move skipAnalytics into an option property instead of a boolean parameter for both getValue and hasFeature. If we chose to only add parameters to hasFeature and not deprecate anything, these would be our options:

1. Add a { fallback: boolean } parameter

// forces you to specify a value for skipAnalytics, which is weird
hasFeature("my_bool", false, { fallback: true })

// looks inconsistent with getValue
getValue("my_feat", { fallback: "foo" }, true)

2. Add a boolean parameter for the fallback

// easy to confuse which is skipAnalytics and which is the fallback
hasFeature("my_bool", false, true)

// easy to confuse with OpenFeature's getBooleanValue
// https://openfeature.dev/docs/reference/concepts/evaluation-api/#basic-evaluation
getBooleanValue("my_bool", true)

// still inconsistent with getValue
getValue("my_feat", { fallback: "foo" })

Putting everything under an option object also lets us add more options if needed without worrying about backwards compatibility or parameter placement/ergonomics.

The new way of using these methods would be:

hasFeature("my_bool", { fallback: true, skipAnalytics: true })
getValue("my_feat", { fallback: "foo", skipAnalytics: true })

Missing from this PR:

• Tests - I didn't see any tests for hasFeature or getValue though
• Docs - wanted to align on the implementation first

[kyle-ssg]

hey @rolodato approach looks fine, added tests and bumped version - let's go ahead with this!

[rolodato]

Nice, thanks! This should be a minor version bump though, not patch

[kyle-ssg]

Ah yep sure.