Feat : log_cli Add RFC3339Nano via cli argument for default output

[steelrain74]

What this PR does / why we need it:
This PR will address a request to add optional subsecond timings to a logcli command line request. By adding a --timestamp=nanos you will output logs in RFC3339Nano instead of RFC3339 for the default output only.
Which issue(s) this PR fixes:
Fixes #9635

Special notes for your reviewer:
This is not breaking for existing customers as this is an optional flag. The default is still RFC3339

Checklist

• Reviewed the CONTRIBUTING.md guide (required)
• [x ] Documentation added
• [x ] Tests updated
• [x ] Title matches the required conventional commits format, see here
  • Note that Promtail is considered to be feature complete, and future development for logs collection will be in Grafana Alloy. As such, feat PRs are unlikely to be accepted unless a case can be made for the feature actually being a bug fix to existing behavior.
• [ x] Changes that require user attention or interaction to upgrade are documented in docs/sources/setup/upgrade/_index.md
• [x ] If the change is deprecating or removing a configuration option, update the deprecated-config.yaml and deleted-config.yaml files respectively in the tools/deprecated-config-checker directory. Example PR

[CLAassistant]

All committers have signed the CLA.