Change CI so it builds everything in release configuration

[latkin]

CI builds everything in debug config today. I see a few problems with that, and only 1 potential benefit.

Cons

• Causes tests to run more slowly
• Prevents all tests from working (fsharpqa and ideunit tests trigger many bogus asserts)
• Build output is slow/asserty, so we can't use it to run full local validation here.

Pros

• Easier to debug if someone is testing the new feature/behavior
  • But to debug, user will still need updated sources...

Changing to release config means tests will execute faster (i.e. CI build will go faster), and CI output can be used to bootstrap full local validation by maintainers.

[dsyme]

Fine by me. (nb. having switched to the paid account we may be able to configure a matrix of builds?)