Set authentication details from env variable

__Proposal:__
Allow disabling initial onboarding and use `apitoken`, `password` from environment instead of db. (Like Postgres).

__Current behavior:__
Users are forced to go into web UI to set up the initial account and tokens are randomly generated. Meaning auto provision isnt possible.

__Desired behavior:__
See proposal

__Alternatives considered:__
No clue, lets discuss

__Use case:__
Why is this important (helps with prioritizing requests)?

This will allow users to specify them when deploying the container, allowing auto provision.

This will also make it easy to rotate api tokens and passwords rotation via secrets and deployment configs. In the scenario where both influxdb and consumer services use secrets supplied by deployment, it makes it super easy to reduce the complexity of keeping db secure and consumers connected,

Another benefit is that in a local development environment where docker-compose is used to run influxdb along with other services, it takes the hassle out of manually setting up influx every time the volume is fresh.

Allow systems testing using fresh influxdb image rather than a pre-provisioned one.

No files, tests, or entry points are named. Start by clarifying the requested provisioning and environment-variable behavior, including how onboarding and credential rotation should work; the issue does not define completion criteria.

Written by the indexing model from the issue text.