remove os.Args hack for backwards compatible arguments

[leehinman]

---

*** Breaking Change ***

Proposed commit message

This PR removes support for single - multi-character command line options. You will need to use -- instead.

For example -environment will no longer work, but --environment will. The single charater options will continue to work, for example -d and -c.

This greatly simplifies our command line argument parsing and makes it much easier to import the beats module into other projects.

Checklist

• My code follows the style guidelines of this project
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have made corresponding change to the default configuration files
• I have added tests that prove my fix is effective or that my feature works
• I have added an entry in CHANGELOG.next.asciidoc or CHANGELOG-developer.next.asciidoc.

Disruptive User Impact

If users have scripts that use the old single - arguments they will need to modify their scripts to use the double --.

Author's Checklist

• [ ]

How to test this PR locally

1. Build a beat
2. make sure that -environment container fails but --environment container succeeds

Related issues

• Closes Remove backwards compatible flag support #42117

Use cases

Screenshots

Logs

[mergify]

This pull request does not have a backport label.
If this is a bug or security fix, could you label this PR @leehinman? 🙏.
For such, you'll need to label your PR with:

• The upcoming major version of the Elastic Stack
• The upcoming minor version of the Elastic Stack (if you're not pushing a breaking change)

To fixup this pull request, you need to add the backport labels for the needed
branches, such as:

• backport-8./d is the label to automatically backport to the 8./d branch. /d is the digit

[mergify]

backport-8.x has been added to help with the transition to the new branch 8.x.
If you don't need it please use backport-skip label and remove the backport-8.x label.

[elasticmachine]

Pinging @elastic/elastic-agent-data-plane (Team:Elastic-Agent-Data-Plane)

[mauri870]

I tested the beats locally as well as searching for all possible flags I could find in the help commands and subcommands of filebeat and metricbeat, couldn't find any leftover flags still using the single dash. LGTM.

[mauri870]

@leehinman I have a question about the fallout of this change. I understand that this is a breaking change but there are numerous Elastic repositories, documentation, and scripts that use the single dash in the commands. How should we address those that are not part of the Beats repository? Is there a plan for handling this?