Draft: Update instructions to set up GDK and Snowplow Micro

What does this MR do and why?

This MR updates the instructions in setting up GDK and Snowplow Micro to clarify that the command gdk psql -d gitlabhq_development should be run in the shell while update application_settings set snowplow_collector_hostname='localhost:9090', snowplow_enabled=true, snowplow_cookie_domain='.gitlab.com'; should be run in psql.

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