Update Dockerfile

[SergeyDjam]

change ELEMENT_WEB_PORT 80 to 8080. For fix start container in podman and docker rootless.

Checklist

• Tests written for new code (and old code if feasible).
• New or updated public/exported symbols have accurate TSDoc documentation.
• Linter and other CI checks pass.
• I have licensed the changes to Element by completing the Contributor License Agreement (CLA)

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[t3chguy]

This would break backwards compatibility in a non-obvious way as all existing functional containers in Docker would break without any error. Vs podman and other quasi-supported environments needing to specify a variable. This is not desirable.