feat(conda): share envs with transformer-based backends (#1465)

* feat(conda): share env between diffusers and bark

* Detect if env already exists

* share diffusers and petals

* tests: add petals

* Use smaller model for tests with petals

* test only model load on petals

* tests(petals): run only load model tests

* Revert "test only model load on petals"

This reverts commit 111cfa97f1.

* move transformers and sentencetransformers to common env

* Share also transformers-musicgen

backend/python/petals/run.sh

@@ -9,10 +9,10 @@ export PATH=$PATH:/opt/conda/bin
 # if source is available use it, or use conda
 #
 if [ -f /opt/conda/bin/activate ]; then
-    source activate petals
+    source activate transformers
 else
     eval "$(conda shell.bash hook)"
-    conda activate petals
+    conda activate transformers
 fi
 
 # get the directory where the bash script is located