Create Snowplow event tracking issue template

What does this MR do?

Create an issue template to help groups consistently create snowplow events.

More details

• Our Product Indicators can only be as "good" as the data we collect. By improving the way we capture requirements will help ensure we capture better data
• Highlight the fields that's available that's in a Snowplow event
• Instrumentation is just the first step, we should immediately create charts in our dashboard to visualize the data
• Self-service in chart creation is not always easy. Provide SQL snippets and examples that PMs can follow

This MR is part of gitlab-com/www-gitlab-com#9125 (closed) to improve the ability to self-service Snowplow data for PMs.