use a base image that already has playwright and its browsers installed

add some test stubs, with one test that is a work-in-progress.

the devcontainer will have pytest-playwright installed so that when
we're writing tests, we can use auto-complete, reference code definition,
etc.

use the 'playwright' service container to run the tests. there is a sample
.env file and a helper script for running tests.

this makes it so they are used any time pytest is invoked from this
directory

this implements it in a simple way that works. there are probably
improvements that can be made, e.g. not waiting 10 seconds for the
enrollment to finish.

mark medicaregov flow test to be skipped.

since the tests-pytest workflow runs from the root level, it was also
collecting Playwright tests.

the tests-cypress workflow was failing because there is no .env file
for the playwright service, but we don't even need that service to
start.

this makes it so it is not started by default.
see https://docs.docker.com/compose/how-tos/profiles/ for more.

to ensure playwright service doesn't prevent other services from
starting if the `playwright/.env` file doesn't exist

keep the scope of this PR small. namely, this PR is for setting up the
environment in which we run and write tests.

figuring out if and how the tests get their values is a separate task
outside the scope of this PR.

further discussion is needed on how exactly we will pass
environment-specific information to the tests.