Utilize global imagePullPolicy for Promtail

Since we now have a global imagePullPolicy value, we should make sure this is passed to the proper places in Promtail to affect its pull policy.

We should also update the document here to list out the overrides if someone wants to set a different pull policy for Promtail.

AC:

• Promtail uses the global pull policy for all containers
• Docs updated to show ways to override Promtail container pull policies

Helpful tips:

• Start by checking the promtail values file and searching for pullPolicy or imagePullPolicy. Note all values locations for this.
• In the BB promtail values add those values and set their value to {{ .Values.imagePullPolicy }} so that they inherit the global (example for jaeger)
• Add those values in a new table row to the table here
• Deploy with promtail enabled, imagePullPolicy: Always in your values, and validate that all containers have an imagePullPolicy set to Always.