feat: add opt-in support for ProxyFroomEnvironment in logcli (#11742)

[devoxel]

This is enabled with the --envproxy flag. This is opt in because for a very small subset of users, it may cause a breaking change. If a user has a proxy url configured but also sets a HTTP_PROXY variable, then this will cause an error in the request.

What this PR does / why we need it:

HTTP_PROXY is a standard approach to configuring CLIs.
In my use-case, it allows me to use an internal tool to do proxy oauth so I can use logcli via CLI behind auth.

Which issue(s) this PR fixes:
Fixes #11742

Checklist

• Reviewed the CONTRIBUTING.md guide (required)
• Documentation added
• Tests updated
• 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.
• Changes that require user attention or interaction to upgrade are documented in docs/sources/setup/upgrade/_index.md
• 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]

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