golang: add note about automatic toolchain switching

[danmilon]

Why

Because in golang, there is a loose coupling between the version specified by the user, and the version that can be used. Essentially it will download any toolchain version automatically.

But users should still be encouraged to keep the selected version updated, in order to have more up to date software.

See also internal ticket: https://linear.app/platformsh/issue/IMG-1785

What's changed

Added a section in both psh and upsun golang docs about this.

What I'm not sure about is how to word the suggestion to keep the golang version in the yaml configuration files up to date.

Where are changes

Updates are for:

• platform (sites/platform templates)
• upsun (sites/upsun templates)

[Kemi-Elizabeth]

@danmilon regarding how to suggest that users should keep their golang version up to date in the yaml. We can use a note block to ensure it catches users attention. Something like:

{{< note >}}

It is important to keep your chosen version of golang updated in your yaml configuration file. This will ensure that you are using the most up to date software for your projects.

{{< /note >}}

[danmilon]

I don't understand what's wrong with CI.

[danmilon]

sorry about the typo. I see you fixed it already, thank you!