Parse`value` as a numeric value for Snowplow events on frontend

What does this MR do and why?

Related to #346998 (closed)

Non-numeric value values silently fail on the collector level. This MR parses the value as numeric before sending the event.

There are no current bugs/problems related to this, and this change is to be future-proof.

How to set up and validate locally

1. Follow the instructions in our docs to enable Snowplow locally, if you haven't done so.
2. Trigger any Snowplow event. That uses the value property
3. Verify the Snowplow testing tool of your choice and you'll be able to see that value is always numeric.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.