Implement IN keyword for local evaluation

[khvn26]

Part of Flagsmith/flagsmith#1595.

NodeJS client's local evaluation mode has to support the IN keyword for segments.

Refer to the Python engine implementation: https://github.com/Flagsmith/flagsmith-engine/blob/4cfb30792feb1fe9f64c082af7e9d64fc1a2f451/flag_engine/segments/models.py#L75-L80

Acceptance Criteria

• When initialized with local evaluation, Flagsmith client correctly evaluates segments defined with the IN keyword.

[novakzaballa]

Tested by creating a segment called "Colors", and adding a condition using the IN keyword as shown below:

In ff_segment flag the value is "segment" and was created a segment override with the "Colors" segment

I used an identity named "user1" and added a new trait {color: "red"}. Also, the value of ff_segment in its segments was changed to "value".

Created an application in Node.js to test the result of getIdentityFlags and check if it is correct, the value obtained when using the getEnvironmentFlags method was also tested.

The results are shown below the following image.

Here you can see that the value of ff_segment is "value"

Here you can see that the value of ff_segment is "segment"

The results are correct in both cases.

In conclusion, the IN keyword seems to be working as expected, and no need for changes was detected.