HCS-CORE: Three way encryption switch

**Detailed Description**
Currently, encryption is either on or off

**Actual Behavior**
Encryption is either on or off, if off, messages are sent in plain text, if on, pair-wise encryption is the default.

**Expected Behavior**
It should be possible to specify:
-No encryption
-Appnet-wide encryption with a single key(AES-256, not ED25519)
-Pair-wise encryption

**Environment:**
- Java: [e.g. OpenJDK 11.0.4]
- Node: [e.g. v12.9.1-x86]
- OS: [e.g. Ubuntu 18.04]
- Version: [e.g. 1.0.1]

**Additional Context**
Add any other context about the problem here. Attach any logs here, if applicable.