Add --markdown output flag for CLI commands

[patrikbraborec]

Description

Currently, some CLI commands support --json for machine-readable output. It would be useful to also support a --markdown flag that outputs results as a Markdown table.

This would make it easy to paste command output into docs, READMEs, GitHub issues, or other Markdown-based contexts.

Applicable commands

The --markdown flag should be added where tabular output is displayed, for example:

• actors search
• runs ls
• secrets ls
• key-value-stores keys
• Any other command that renders a table

Expected behavior

Commands with the --markdown flag should output results formatted as a Markdown table, e.g.:

| Name | Description | Users (30d) | Pricing |
|------|-------------|-------------|---------|
| Web Scraper (apify/web-scraper) | ... | 123 | Free |

[patrikbraborec]

Closing as superseded by #1061 which covers this as part of a broader structured output effort.