Support AES-256 for internal encryption

[AqeelMuhammad]

Description

Currently in APIM, it works with the RSA asymmetric encryption with RSA/ECB/OAEPwithSHA1andMGF1Padding. We need to change it for AES/GCM/NoPadding to support symmetric key encryption by default.

Below are some identified points where it uses encryption internally.

1. Backend security secrets - Publisher Portal
2. Key Manager secrets - Admin Portal
3. Gateway secrets - Admin Portal
4. API Policy secrets - Publisher Portal
5. Access Tokens - Developer Portal
6. Mediation Policy secrets - Publisher Portal
7. User store config credentials - Carbon Console

Version

4.7.0