Move jenkins password to secret manager

[cliffano]

Jenkins password is currently a user configuration (specified in YAML), this should be moved to AWS resources as a secret on AWS Secrets Manager.

This needs to be optional (resource created with a condition), and only retrieve secret from AWS Secrets Manager if the password is not supplied in YAML file.
This is to allow users who don't currently approve the use of AWS Secrets Manager to use the YAML user config as a fallback mechanism.