[prometheus-json-exporter]: Allow additional container args and service monitor relabelings

[faisal-khalique]

What this PR does / why we need it

• Adds the option to pass arguments to the container. Could be needed for many reason. For example collecting logstash metrics with many pipelines where the pipeline definitions vary based on environment. Having the option of providing argument --config.file will greatly simplify such deployments. Considering future use cases, adding an array instead of just specifying the argument --config.file now
• Add additional relabelings for service-monitor which can be used to drop unwanted labels from the metrics like container, pod, etc.

Special notes for your reviewer

Checklist

• DCO signed
• Chart Version bumped
• Title of the PR starts with chart name (e.g. [prometheus-couchdb-exporter])

[faisal-khalique]

@zanhsieh - can you please check this PR?