Configurable edgex secret store

[farshidtz]

PR #20 adds the support for edgex-security option set to on/off. This is fine in most settings but is not extensible to allow other ways to provide the secret. Moreover, it isn't so intuitive because it sets the "edgex-security" to off even though the redis credentials may be passed via other means to allow secure connections. What it really does is to disable redis credentials setup. The redis credential setup involves (1) querying credentials from a vault (local, default port) using the vault token provided by the content interface and (2) injecting credentials into config files.

We can get inspiration from toml secret store section in configuration files of other services. E.g. device-mqtt:

[SecretStore]
Type = "vault"
Host = "localhost"
Port = 8200
Path = "device-mqtt/"
Protocol = "http"
RootCaCertPath = ""
ServerName = ""
# Uncomment to seed service secrets file
# SecretsFile = "/tmp/edgex/secrets/device-mqtt/secrets.json"
DisableScrubSecretsFile = false
TokenFile = "/tmp/edgex/secrets/device-mqtt/secrets-token.json"
    [SecretStore.Authentication]
    AuthType = "X-Vault-Token"

[farshidtz]

No longer relevant. EdgeX secret store usage is now disabled with config.edgex-security-secret-store=false.