Support custom Composer repositories for extension version checking

[pariweshsubedi]

Please describe the feature you would like to see implemented.

Problem

Shopmon currently checks extension versions against the Shopware Store API. Extensions installed from private Composer repositories (e.g. Packeton, Private Packagist, Satis) never get a latestVersion, so update notifications don't work for them.

Proposed Solution

Allow shops to configure custom Composer repositories in the Edit Shop page. During scraping, after the standard Store API check, query these repositories for any extensions still missing a latestVersion.

Features

• Support for Composer v1 (inline) and v2 (lazy provider) repository formats
• Authentication options: none, HTTP Basic, Bearer token
• Credentials encrypted at rest using the existing APP_SECRET encryption

[shyim]

Good idea. I thinking about providing inside Shopmon also a Composer repository server, could be a good addition to that.