Update Assignment requirements for `tier_badge` experiment

What does this MR do and why?

Resolves #408370 (closed) and #407831 (closed).

This MR modify the candidate requirement for the tier_badge experiment and also include the namespace id in the assignment event to prepare for restarting the experiment.

The updated candidate requirement is we only want to include namespaces that are still on free plan, without trial on the 14th day after created.

Screenshots or screen recordings

Sample snowplow assignment event with namespace id included:

How to set up and validate locally

1. Setup gdk to simulate SaaS and restart gdk
2. Create a top-level group
3. Open a new gdk console (gdk rails c)
4. Inisde the console

# Enable experiment
Feature.enable(:tier_badge)

# Modify the group to be created 14 days ago
Group.last.update_attribute(:created_at, 14.days.ago)

1. Visit the group page and observe the badge, and the popover

MR acceptance checklist

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