Add --emit-options/--no-emit-options flags to pip-compile

[atugushev]

Description

A switcher to turn off all options in the compile output.

Rationale

1. It might be helpful for users who have pip.conf and don't want to pass any options to the compile output. Yes, they can switch off some of the options with --no-emit-trusted-hosts and --no-emit-find-links, but there is no option to turn them all off.

2. Also, it's pretty useful for the tests to check the exact resolver output. For example, instead of:

out = invoke(cli)
assert "small-fake-a==0.1" in out.stderr

check the complete result and make sure that there are no side dependencies

out = invoke(cli, ["--no-annotate", "--no-emit-options"])
assert out.stderr.splitlines() == ["small-fake-a==0.1"]

Changelog-friendly one-liner: Add --emit-options/--no-emit-options flag to pip-compile.

Contributor checklist

• Provided the tests for the changes.
• Gave a clear one-line description in the PR (that the maintainers can add to CHANGELOG.md on release).
• Assign the PR to an existing or new milestone for the target version (following Semantic Versioning).

[ssbarnea]

@atugushev Can you please rebase it and eventually mark it as draft if is not passing CI? Thanks.

[ssbarnea]

@atugushev LGTM but please fix conflicts.