Allow reading payload parameters from secret / parameter store

[toshke]

In case of authorization headers needing to be sent to HTTP(s) endpoint - they should be stored in secret store, rather than passed unencrypted as payload to lambda function. Suggestion is that if any value in payload is in following forms

• aws:smps("path")
• aws:sm("store.key")

They should be replaced with actual secret value from AWS System Manager Parameter Store (first form), or AWS Secrets Manager (2nd form).