specs,schedulers: add VolumeMount

[d4l3k]

This adds a new mount type volume which allows mounting named volumes onto the container environment. It also updates the documentation for each scheduler to include mount support.

Per scheduler:

• Docker: named volume
• Kubernetes: PersistentVolumeClaimVolume
• AWS Batch: EFS ID - I'm a little hesitant on this since batch may add other volume types such as FSx etc

Closes #422

Test plan:

added unit tests

CI

(torchx) tristanr@tristanr-arch2 ~/D/torchx-proj> torchx run --scheduler local_docker --wait --log dist.ddp -j 1x1 --script foo.py --mount type=volume,src=fo
o2,dst=/tmp
torchx 2022-03-15 17:23:42 INFO     loaded configs from /home/tristanr/Developer/torchx-proj/.torchxconfig
torchx 2022-03-15 17:23:42 INFO     Building workspace: file:///home/tristanr/Developer/torchx-proj for role[0]: foo, image: ghcr.io/pytorch/torchx:0.1.2dev0
torchx 2022-03-15 17:23:44 INFO     Done building workspace
torchx 2022-03-15 17:23:44 INFO     New image: sha256:82c6b984bd64c9c38aa86c4cb855b88ce3d62c65c50519372cd63f382d4bb71c built from workspace
local_docker://torchx/foo-nn5vkq7sc2xz9c
torchx 2022-03-15 17:23:45 INFO     Waiting for the app to finish...
foo/0 [0]:hello
torchx 2022-03-15 17:23:51 INFO     Job finished: SUCCEEDED
(torchx) tristanr@tristanr-arch2 ~/D/torchx-proj> docker volume ls | rg foo2
local     foo2

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[codecov]

Codecov Report

Merging #426 (e6ac408) into main (354d26e) will increase coverage by 0.00%.
The diff coverage is 90.32%.

@@           Coverage Diff           @@
##             main     #426   +/-   ##
=======================================
  Coverage   94.40%   94.41%           
=======================================
  Files          67       67           
  Lines        3805     3829   +24     
=======================================
+ Hits         3592     3615   +23     
- Misses        213      214    +1     

Impacted Files	Coverage Δ
torchx/components/dist.py	79.54% <ø> (ø)
torchx/specs/__init__.py	96.15% <ø> (ø)
torchx/schedulers/aws_batch_scheduler.py	84.18% <80.00%> (+0.85%)	⬆️
torchx/schedulers/docker_scheduler.py	95.74% <80.00%> (-0.46%)	⬇️
torchx/schedulers/kubernetes_scheduler.py	92.64% <80.00%> (-0.36%)	⬇️
torchx/specs/api.py	99.04% <100.00%> (+0.03%)	⬆️

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