Add Plex config flow support (#26548)

* Add config flow support

* Log error on failed connection

* Review comments

* Unused errors

* Move form to step

* Use instance var instead of passing argument

* Only share servers created by component

* Return errors early to avoid try:else

* Separate debug for validation vs setup

* Unnecessary

* Unnecessary checks

* Combine import flows, move logic to component

* Use config entry discovery handler

* Temporary lint fix

* Filter out servers already configured

* Remove manual config flow

* Skip discovery if a config exists

* Swap conditional to reduce indenting

* Only discover when no configs created or creating

* Un-nest function

* Proper async use

* Move legacy file import to discovery

* Fix, bad else

* Separate validate step

* Unused without manual setup step

* Async oops

* First attempt at tests

* Test cleanup

* Full test coverage for config_flow, enable tests

* Lint

* Fix lint vs black

* Add test init

* Add test package requirement

* Actually run script

* Use 'not None' convention

* Group exceptions by result

* Improve logic, add new error and test

* Test cleanup

* Add more asserts

script/gen_requirements_all.py

@@ -110,6 +110,7 @@ TEST_REQUIREMENTS = (
     "paho-mqtt",
     "pexpect",
     "pilight",
+    "plexapi",
     "pmsensor",
     "prometheus_client",
     "ptvsd",