bug: fix type discrepancy of IFilter with implementation

[weboko]

Description

Currently IFilter interface is missing definition of createSubscription method from here but hast implementation of it here

Expected Behavior

Type definition should be aligned with implementation.

Steps to Reproduce

N/A

Environment Details

Version: @waku/sdk: 0.29.0

[weboko]

Todo:

• check if we need to define createSubscription as we want consumers use subscribe method;
• check docs website to see if it is not advertised there;

[weboko]

Closing as Filter API is under review.