Add Minimum Spanning Tree in Go

[rzuckerm]

To request a new code snippet, please fill out the following:

Project name: Minimum Spanning Tree
Project link: https://sampleprograms.io/projects/minimum-spanning-tree
Language: Go

The project link must be a link to a project on the Sample Programs Website project list.
If you would like to add a new project to the Sample Programs Website,
please first make a pull request to the Sample Programs Website.