[2.x] [tests] implement a solution to run `make:reset-password` command in tests

[jrushlow]

We introduced a handful of test fixtures in #319 (basically the files make:reset-password generates) so we can run tests against a "real" symfony webapp. This is great, but maintaining fixtures is not ideal. We should:

• Remove the fixtures (or atlease as many as we can)
• call make:reset-password right after we call make:user in the functional test
• run tests against the generated code

The reason why this was not done in #319 - make:reset-password requires user input to successfully execute. To simulate that in a test, we need to:

1. Create a "test" process
2. stream the contents of an array of user input e.g. ['question 1 input', 'question 2 input']
3. execute the test process to run the test

We do this in MakerBundle -> https://github.com/symfony/maker-bundle/blob/main/src/Test/MakerTestEnvironment.php#L333 But that code is internal (and should stay that way for now).

Ideally, we would have a symfonycasts/test-helpers repo (insert better name here) that is "internal" / doesnt provide BC guarantees, etc.. that we can use in reset-password, verify-email, etc... to handle the nuts and bolts of bootstrapping a "app" test.