Track which to-do item reasons users filter by

What does this MR do and why?

• This MR adds missing Snowplow tracking on filtering to-dos by reason (e.g. "Review requested", "Assigned", etc.)
• The Growth team is exploring making filtering by reason more visible in the UI, but we have no visibility of what reasons are selected

This MR adds tracking to two locations:

To-do list	Personal homepage

Personal homepage tracking additions

• open_todos_filter_dropdown_on_homepage, which fires when the dropdown opens
• filter_todos_on_homepage, which fires on selection, with added property to capture the filter

To-do list tracking additions

• adds a property on the existing filter_todo_list to capture the filter reason

Validate locally

Set up tasks

1. Install the Snowplow Analytics Debugger Chrome browser extension.
2. Ensure Docker is installed and working
3. Enable Snowplow Micro in GDK
4. Observe in Snowplow Debugger that the event is tracked (gif example below)

Personal homepage

1. Visit the personal homepage (e.g. click on the GitLab logo in the top left of the screen)
2. Click on the dropdown next to "Items that need your attention" that says "Everything"
3. Select a different reason, e.g. "Review requests"
4. Confirm that analytics show up in Snowplow Debugger

To-dos page

1. Visit the to-dos page (/dashboard/todos)
2. Use the filter bar to filter by reason
3. Confirm that analytics show up in Snowplow Debugger

MR acceptance checklist

Evaluate this MR against the MR acceptance checklist.