Make sure `APPMAP_RECORD_REQUESTS=true` will generate request recordings
when running tests. Previously, it was ignored, and request recordings
were never generated when tests were run.

Combine APPMAP_RECORD_PYTEST and APPMAP_RECORD_UNITTEST into
APPMAP_RECORD_TESTS.

Also, fix a typo.

Recording is no longer enabled by default. It is now necessary to run scripts with
appmap-python, or explicitly set APPMAP=true

BREAKING CHANGE: disable record by default

It doesn't make sense (and doesn't work) to try to capture other
recording types when the user says they want a process recording (by
setting APPMAP_RECORD_PROCESS=true).