[newrelic-logging] feat: allow overriding command

[woehrl01]

Is this a new chart

What this PR does / why we need it:

This PR allows to overriding the command. This can be useful to not specifying the output module if you want to use the nrlog output plugin of fluentbit directly.

Which issue this PR fixes

(optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close that issue when PR gets merged)

• fixes #

Special notes for your reviewer:

Checklist

[Place an '[x]' (no spaces) in all applicable fields. Please remove unrelated fields.]

• [ ] Chart Version bumped
• [ ] Variables are documented in the README.md
• [x] Title of the PR starts with chart name (e.g. [mychartname])