Un-deprecate `influxd print-config` or suggest more suitable replacement

[kbolino]

Proposal:

Clarify how to produce a default configuration file for new setup. Some possible avenues:

1. Un-deprecate influxd print-config
2. Rename print-config subcommand to avoid confusion (assuming that was the reason for deprecation)
3. If a suitable alternative already exists, suggest it along with or instead of influx server-config
4. If best practice has changed entirely, at least update the documentation for the docker image (and elsewhere, if appropriate) accordingly

Current behavior:

The docker image documentation's configuration section recommends influxd print-config to obtain the default configuration. When you actually do this, however, InfluxDB 2.4.0 warns:

Command "print-config" is deprecated, use the influx-cli command server-config to display the configuration values from the running server

Okay, very well, but if you do what that recommends (and I'm not sure if this is intentional, but influx-cli is misleading, as the CLI is called simply influx):

Error: failed to retrieve config: Get "http://localhost:8086/api/v2/config": dial tcp 127.0.0.1:8086: connect: connection refused

And looking at the --help output it seems that influx server-config can only retrieve actual config from a running server.

Desired behavior:

A quickstart config file is useful for, well, getting started quickly. The docs for the deprecated influxd print-config option also make it sound quite useful for understanding the effect of various administrative changes (emphasis mine):

Print config (in YAML) that the influxd server would use if run with the current flags/env vars/config file.

Whereas the recommended replacement influx server-config seems only to be able to produce the configuration that a server is actually using. The use cases don't overlap in my opinion.

Alternatives considered:

Besides the recommended replacement, I also tried to find alternatives through the online documentation but a couple of searches I tried were not fruitful.

Use case:

1. Quick start with sane defaults
2. Understanding the impact and inter-relationship of environment variables, flags, and file-based config options