[improve][CLI] show environment variables in CLI and optimize them to `--config-file` argument

### Search before asking

- [X] I searched in the [issues](https://github.com/apache/pulsar/issues) and found nothing similar.

### Motivation

I've separated the code improvements from https://github.com/apache/pulsar/issues/19492 (created by @visortelle) and discussed them with @codelipenghui as below.

### 1. Show `enviroment variables` for `pulsar-admin` and `pulsar-client` on CLI

Contexts:

I've double-checked the current behavior:

- `pulsar-perf -help` shows `environment variables`

- while `pulsar-admin -help` and `pulsar-client` do not show `environment variables`

To give users complete info,`environment variables` should be shown on `pulsar-admin` and `pulsar-client` CLI as well.

### 2. Implement `--config-file CLI` argument instead of `environment variables`.

@visortelle has explained it in https://github.com/apache/pulsar/issues/19492

### Solution

_No response_

### Alternatives

_No response_

### Anything else?

_No response_

### Are you willing to submit a PR?

- [ ] I'm willing to submit a PR!

Start by comparing the help output of the mentioned pulsar-perf, pulsar-admin, and pulsar-client CLI entry points, and read the referenced issue 19492 for the config-file requirements. Done means pulsar-admin and pulsar-client show their environment variables and support the requested --config-file argument.

Written by the indexing model from the issue text.