[RFC] EnvVarProcessor using AWS Secrets Manager

Would anyone use a EnvVarProcessor that uses the AWS Secrets Manager?

What I'm thinking is to implement EnvVarProcessorInterface and create a awsSecret key that takes a SecretId, and optionally a versionID and / or versionStage and resolves this in runtime. Then in config, you can use a string similar to this to use amazon secrets in the config.

```
parameters:
db_dsn: "mysql://db_user:%env(awsSecret:db_password)%@127.0.0.1:3306/db_name"
```

Thoughts? Does anyone want this? Would such a feature be merged?

Start by reviewing EnvVarProcessorInterface and the proposed awsSecret configuration syntax in the issue. The RFC does not name implementation files, tests, or acceptance criteria, so clarify intended usage, supported secret version options, and what would count as a mergeable feature before coding.

Written by the indexing model from the issue text.