Made CASC_SSM_PREFIX work properly with parameters stored in Secrets Manager

[galargh]

Description

According to this guide it is possible to reference Secrets Manager from Parameter Store. To do so parameter key must be prefixed with /aws/reference/secretsmanager/. This PR ensures that /aws/reference/secretsmanager/ prefixed is respected even if CASC_SSM_PREFIX variable is set.

Example

Given the following casc config entry

- credentials:
      - string:
        id: "cred-id"
        secret: /aws/reference/secretsmanager/my.parameter.name

and the following CASC_SSM_PREFIX value

export CASC_SSM_PREFIX='my.prefix'

the CASC SSM Plugin would try to retrieve a parameter with the following name

/aws/reference/secretsmanager/my.prefix.my.parameter.name

Testing

• mvn test

[galargh]

@patbos Have you had a chance to have a look at this proposal?

[galargh]

@patbos I was wondering what your thoughts are on this one.

[mwos-sl]

Any chances to have this merged? We need to keep our own releases because of that :(