Set fallback port for underspecified endpoints

[dominiklohmann]

📔 Description

Sets a fallback port of 42000 when the vast.endpoint option is set, but does not contain a port.

📝 Checklist

• All user-facing changes have changelog entries.
• The changes are reflected on docs.tenzir.com/vast, if necessary.
• The PR description contains instructions for the reviewer, if necessary.

🎯 Review Instructions

Run vast -e localhost start with and without this change to verify this works.

[mavam]

Makes sense overall.

Is it still possible to explicitly specify 0 as port to get a random port that is available on the system?

[mavam]

I tested this locally and it works. For example, vast -e 0.0.0.0 start no longer opens a random high-level port.