[prometheus-postgres-exporter] Allow override of container name

[not7cd]

What this PR does / why we need it

When using this chart as dependency, you may want to use alias.
This alias may use camelCase as this is a common convention in values.yaml.
This will result in an error as expected name must conform to RFC 1123.

Example

# Chart.yaml
dependencies:
- name: prometheus-postgres-exporter
  alias: postgresExporter
  repository: "https://prometheus-community.github.io/helm-charts"
  version: 5.3.0
  condition: postgresExporter.enabled

# values.yaml
postgresExporter:
  enabled: true
  nameOverride: "prometheus-postgres-exporter"
  image: ...

Results in

# deployment.yaml
metadata:
  name: release-name-prometheus-postgres-exporter
  labels:
    chart: postgresExporter-5.3.0
    app: prometheus-postgres-exporter
spec:
  template:
    spec:
      containers:
        - name: postgresExporter

Which issue this PR fixes

None, this could be converted to an issue, but the fix seemed obvious.

Special notes for your reviewer

Checklist

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