Support Filtering by Metadata Key Only in Lists and Segments

🔍 Problem Statement

Currently, Lists and Segments require both a metadata key and metadata value when filtering by metadata. This prevents us from using metadata as a reporting and logging tool, as our metadata values are unique for each customer interaction while the metadata keys identify the type of record being logged (e.g., MISSED_ISSUE, PAID_DUTY, RENEWAL). As a result, we are unable to segment or export records based on the existence of a metadata key alone.

💡 User Story

As a user, I want to filter Lists and Segments by metadata key only, so that I can identify, segment, automate, and export all records associated with a specific metadata key regardless of the metadata value.

🎯 Definition of Done

✔ Users can filter Lists and Segments by metadata key without specifying a metadata value.

✔ The filter returns all records that contain the specified metadata key, regardless of its value.

✔ Existing metadata key + value filtering continues to function as it does today.

✔ The new filtering option is available for both Lists and Segments.