Add ability to include GTM environment query parameters

I found some issues with the patch:

+function cookiebot_gtm_prepare_query() {

This is missing a documentation block.

Also , as it is a helper function, I think it is a convention to rename it to _cookiebot_gtm_prepare_query()

+  // Prepare extra query parameters for the GTM script URL.
+  $query = '"' . cookiebot_gtm_prepare_query() . '"';

Concatenating a function with some strings looks weird. I'd do something like:

$query = cookiebot_gtm_prepare_query();
$query = '"' . $query . '"';

But maybe there is a more elegant solution for this.

I was finding that the with Matteo's patch the ampersands in the GTM script were being rendered as encoded (&).

I notice that when the html_tag was being rendered, it was being run through a sanitising function before setting that new value as the eventual markup.

In our module, if you set the #value of the html_tag as markup then it bypasses the sanitisation.

I'm not sure if this is the right thing to do but it allowed us to move forward.

I realise I accidentally included a change from a seperate patch which altered the script to use 'defer' rather that 'async'. Here's an update without that.

I realised I needed to do something similar to the noscript output of this module.

I have tested the latest patch and I also applied changes as suggested by batigolix. The code was released in version 1.0.14.