Add jdbc_password_filepath

[TheFrozenFire]

In the jdbc input plugin, there is a parameter called jdbc_password_filepath which is very convenient when deploying pipelines in Kubernetes, as the credentials for the JDBC connection can be mounted from cluster secrets.

It would be very helpful to have this parameter on the jdbc_streaming filter.

[TheFrozenFire]

Scratch that. Since logstash 5.5.0 there has been environment variable interpolation support, which negates the value of having a specific config option for this sort of thing.

One can specify extraEnv in the logstash helm chart values to create environment variables sourced from secrets.