Go: add [go-test].timeout_default

[Eric-Arellano]

Follow up to #13707. Add these options:

• [go-test].timeout_default, which you fall back to if the field is not set. Defaults to not being set, meaning no timeouts.
• [go-test].timeout_maximum
• [go-test].timeouts to toggle the feature entirely. Useful when debugging to disable timeouts

These have worked well for Python.

While at it, also add to Shell.

[tdyas]

@Eric-Arellano: Should the Go timeout respect the global [test].timeout_default and [test].timeout_maximum options instead?

[Eric-Arellano]

Ah yeah, this ticket is stale from before that improvement. Good catch

[tdyas]

Looks like this already done due to TestTimeoutField.