Add sub_path_expr to volume mount options

[jk-f5]

Description

Added ability to declare sub_path_expr in volume mounts. I more or less just grepped for sub_path and added the equivalent code for sub_path_expr. I'm a bit shocked that this hasn't been added already.

Acceptance tests

• Have you updated an existing acceptance tests for the functionality being added?
• Have you run the acceptance tests on this branch?

Output from acceptance testing:

$ make testacc TESTARGS="-run '^TestAccKubernetes(Deployment|Pod|ReplicationController)'"
...
PASS

Release Note

Release note for CHANGELOG:

Enhancement
- Added ability to declare sub_path_expr in volume mounts. 

References

Community Note

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[hashicorp-cla-app]

All committers have signed the CLA.