Support non-kubernetes deployment

Are you willing to contribute it (Yes/No):yes

**Describe the feature and the current behavior/state.**
Currently, the service always tries to read and write to kubernetes secret. This feature will support reading and writing to a local file which allows the service to be used in non-kubernetes environment.

This will simply be done by adding an environmental variable what the desired storage type is.
**Will this change the current API? How?**
No
**Who will benefit with this feature?**
Anyone in a non-kubernetes environment that would automatically generate pgp key for use with the pgp service.
**Miscellaneous Information**

Start by locating the service code that reads and writes Kubernetes secrets; no specific files or tests are named in the issue. Trace how configuration is currently selected, then verify the storage-type environment variable can select local-file behavior without changing the API. Done means non-Kubernetes deployments can read and write the PGP key locally while existing Kubernetes behavior remains available.

Written by the indexing model from the issue text.