Allow to filter by squawk

[Thrasher2020]

Is your feature request related to a problem? Please describe.
Ability to filter the list based on a specific squawk code - I would like to use it in conjunction with an alert that lets me know when planes squawk 7001 near me. These are normally military entering the low fly zone.

Describe the solution you'd like
Add another config entry to the card to allow filtering by squawk code.

Describe alternatives you've considered
Tried creating a second sensor and filtering but the end result isn't parse able by the FR24 card.

Additional context
Add any other context or screenshots about the feature request here.

[fratsloos]

This is related to #12. Filtering will be possible in the future. I'm not working on it yet, but I hope to do that somewhere in the last quarter of 2022.