added diagram to explain ingress and encryption

Summary:
Documenting Network Encryption and Ingress

Click here to see the doc:
https://repo1.dso.mil/platform-one/big-bang/bigbang/-/blob/network_encryption_and_ingress/docs/understanding_bigbang/network_encryption_and_ingress_diagram.md

Should Close:

• https://repo1.dso.mil/platform-one/big-bang/bigbang/-/issues/370
• https://jira.il2.dso.mil/browse/BBOI-693
• https://jira.il2.dso.mil/browse/BBOI-655