Update zitadel quickstart script to support multiple webservers and PostgreSQL

[abulazif]

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Enhance the script for self-hosting by adding support for running multiple webservers alongside PostgreSQL instead of CockroachDB. Additionally, it modifies the script to change the SSL port from the default 443 to a customizable port to accommodate different setups.

• Include instructions for installing and initializing PostgreSQL.
• Update configuration to use a customizable SSL port.
• Update README.md with clear instructions on customizing the SSL port and running the script.

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