utils: Added external process

[michael-redpanda]

PoC (which may be promoted to a full PR) of the external process utility

Backports Required

• [X] none - not a bug fix
• [ ] none - this is a backport
• [ ] none - issue does not exist in previous branches
• [ ] none - papercut/not impactful enough to backport
• [ ] v24.2.x
• [ ] v24.1.x
• [ ] v23.3.x

Release Notes

• None