Replace GTM variable {{CJS - combine data-link position and group }} with non-JS version

[stephaniehobson]

** ⚠️ Wait for July 2024 ⚠️ **

In UA when we tracked the link_click event we used both data-link-position and data-link-group values. In GA4 we are going to just have data-link-position. At the moment there is some custom JS in GTM to combine the separate values.

When we remove the UA code we can edit the value of data-link-position to combine the two values in bedrock, remove the data-link-group attribute and do away with the custom JS variable in GTM.

• Migrate the value of data-link-group into the data-link-position attributes in bedrock
• Delete data-link-group attributes from bedrock
• Remove the custom JS from GTM in favour of the data-link-position value