Update hosted envs (#3818)

* add guide for dev builds

* hosted env file for openmm-8 beta

* explain how to host an env

* add a namespace to support different os

* pin all the versions

* add version pins and env name

* Added pytest

* update envs

devtools/hosted-envs/openmm-8-beta-linux.yaml

@@ -10,4 +10,5 @@ dependencies:
   - openmm-ml==1.0beta
   - openmm-torch==1.0beta
   - nnpops==0.2
+  - torchani==2.2.2
   - pytest
\ No newline at end of file

devtools/hosted-envs/openmm-8-beta-mac.yaml

@@ -9,4 +9,5 @@ dependencies:
   - openmm==8.0.0beta
   - openmm-ml==1.0beta
   - openmm-torch==1.0beta
+  - torchani==2.2.2
   - pytest