feat: [FFM-12306]: Enhance caching key

[knagurski]

This PR adds the new deriveKeyFromTargetAttributes cache config option. This allows the use of target attributes when building up the key that's used to store and retrieve evaluations from the cache.

// use all attributes when deriving key
const client = initialize(apiKey, target, {
  cache: {
    deriveKeyFromTargetAttributes: true
  }
})

// use subset of attributes when deriving key
const client = initialize(apiKey, target, {
  cache: {
    deriveKeyFromTargetAttributes: ['attributeA', 'attributeB']
  }
})