Support activation of Test2::Plugin::BailOnFail by env var

[dboehmer]

I often happen to run longer test files with some failing test statement in the middle. To see the relevant section of the test output I keep scrolling up in my terminal until I finally edit the test and add use Test2::Plugin::BailOnFail. But I don’t want to add this to any of my test file permanently, e.g. because they should run to the end in CI.

Could we instead add a feature to Test2::V0 to activate the plugin automatically if some env var like TEST2_BAILONFAIL is set to a true value?

[exodist]

I think a better option would be to add and env var TEST2_ENABLE_PLUGIN that takes a comma separated list of plugins to enable.

Examples:
TEST2_ENABLE_PLUGIN=BailOnFail
TEST2_ENABLE_PLUGIN=BailOnFail,UTF8,+My::Plugin

I also think this env var should be recognized by Test2::API so even if you use Test::More or another Test2 bundle other than V0 you can still use this.