supabase start: update text to show that it's starting containers

[kiwicopple]

Chore

Describe the chore

The current setup is a bit slow when running supabase start.

I think we can imrpove it by either:

a. don't check for image updates (and add a command to pull them as/when needed)
b. add a command for skipping the check. eg supabase start --skip-images

a is preferable as it's less typing, but probably more complicated on the initial supabase start

[soedirgo]

It's actually pulling images only when necessary - the slow part is starting containers. I think I can make the status clearer on the spinner on this one.