Relocation of our Go plugin source code.

[Ferroin]

As part of trying to make Netdata easier to maintain and work with, we are moving our Go data collection plugin (go.d.plugin) from a separate repo (https://github.com/netdata/go.d.plugin) into the main netdata repo. #17005 is the final step of this from an end user perspective, and once that is merged all handling of the Go plugin will be through the main repository.

If you use our Docker images, static builds, or our official native packages, this change should not affect you at all.

If you build the Netdata agent locally, you will need a local copy of the Go toolchain (currently v1.21 or newer is required) to build the plugin, and updates and installs will take longer than they did previously. If you do not already have a suitable Go toolchain installed and do not explicitly disable the Go plugin (using either --disable-go or --disable-plugin-go), the installer or updater will automatically pull in a suitable copy of the toolchain in most cases, and will automatically disable building the plugin and log a warning if they cannot do so for some reason.

If you are a third-party package maintainer, this adds a build-time dependency on a working implementation of the Go language, currently requiring Go v1.21 or newer. You can explicitly disable the plugin by adding -DENABLE_PLUGIN_GO=False to the arguments you pass to cmake. Note that this also means we will stop providing pre-built Go executables as part of releases, and that we are likely to add additional components written in Go in the future, so disabling the plugin should be seen as a stop-gap until proper support is possible, not a long-term solution.