[gatsby-plugin-google-tagmanager] Custom events object for page change, currently limited to only change the event name

[mustofa-binary]

Description

The Google Tag Manager plugin currently has a default push event on a page change, we can indeed configure the event name, however, we want to add another properties to the push event object, for e.g:

data.push({ event: `gatsby-route-change`, is_logged_in: true }) 

To allow more flexibility, it would be great for users to add their own event object for this rather than only event name.

btw, the labels should be feature or enhancements, i dont see the option when i try to open new issue, so its default to bug 🙏