Implement encryption of interface credentials

Overview:
For security reasons we need to store interface credential password encrypted with possibility of decription.
The main idea is to generate encryption key on each POST interface credential request, encrypt received password before saving it to DB, and save encryption key to the secure storage. On each GET interface credential request: pull encryption key and return response with decrypted password.

One of the secure stores could be used for this purpose.

Acceptance Criteria:

• password is encrypted on POST and PUT interface credential request
• password is decrypted on GET interface credential request
• Unit tests are updated
• API tests are updated