configuration options

[tgross]

Provide config flags or config file parsing for vault behavior (with sensible defaults, and documentation):

• gRPC tunables:
  • port and address
  • shutdown timeout
• read stream tunables:
  • stream timeout
  • stream batchsize
• feed configs:
  • directory location of feeds
  • feed options, particularly key management
  • replication config feed replication #5