Custom script support for stack auto-start

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Summary

Add option to use a custom initialization script for auto-starting compose stacks instead of the default start, allowing users to control service startup process.

Detailed description

For stacks where startup order is critical or where separate pre-setup is necessary, this can cause initialization failures.

Adding an optional "Custom Start Script" field in the stack settings (alongside the existing autostart toggle) where users can specify a path to a custom shell script would be beneficial. When autostart is enabled and a custom script is provided, execute that script instead of the default starting behaviour.