Setup Go module

[gregtyler]

Purpose

Since Go 1.16, modules are enabled by default and the loose getcreds.go script doesn't work. (There's a workaround involving disabling modules, but that's not good long term.)

Approach

This change adds a go.mod and go.sum file to initialise the module. As Go cannot run scripts form outside the module's root directory, the PR also changes the documentation and automation scripts to cd properly.

Learning

Took a bit of digging to initially identify why the script wasn't working any more. To disable the must-be-a-module rule, you can use go env -w GO111MODULE=on. But note that this is a permanent non-scoped change, so make sure to switch it back to avoid problems in other Go code.

Checklist

• I have performed a self-review of my own code
• I have added relevant logging with appropriate levels to my code
  • N/A
• I have updated documentation where relevant
• I have added tests to prove my work
  • N/A
• I have run the integration tests (results below)

[cooperaj]

Works for me. I've had to use it as I reset my env.

[gregtyler]

@cooperaj Are you okay to approve this?