NGINX Plus: Allow for configuring `enforce_initial_report` field

[sjberman]

As a potential NGINX Plus user,
I want to have a grace period for my initial licensing report,
So that I can validate NGF as a PoC without restriction.

NGF currently sets enforce_initial_report off; for NGINX Plus data planes when initially installing, but once the first configuration is sent from the control plane to the data plane, this directive is removed (defaulting to on). Users should be able to set this field themselves for other circumstances, like PoC testing or exemptions.

For reference: https://nginx.org/en/docs/ngx_mgmt_module.html#enforce_initial_report

Acceptance

• add a CLI argument to the controller to enable or disable the initial report enforcement
• set the field in the nginx config based on the user input
• the existing bootstrap config that sets this field to off should be left as-is to ensure startup succeeds
• update the cli flag document
• add helm chart flag to the existing nginx plus usage section

Dev Notes

• This cli option can fit alongside the existing nginx plus usage cli options we already have