add context.register_envs to control whether environments are registered to environments.txt or not

[jaimergp]

Closes #2783

xref conda/conda#12924
xref conda/constructor#716

[JohanMabille]

Thanks!

[jonashaag]

Is there any good way to write a test for this?

[wolfv]

I love this but we need to wire it up, right?
It should probably be accessible from

• python
• CLI
• Environment variable
• Config

cc @JohanMabille

[jaimergp]

Is there any good way to write a test for this?

This is what conda has: https://github.com/conda/conda/blob/adcf8ef6f268cf8f77cf2b433d1ccf56fad94bdb/tests/core/test_envs_manager.py#L32

And in constructor: https://github.com/conda/constructor/blob/cf0f466bc72c1b3b2d2bf435046b8686c335a52c/tests/test_examples.py#L449