Support Google Consent mode in gatsby-plugin-google-tagmanager

[aileenrose]

Allow script tag to be updated with data-cookieconsent="ignore" to support the Google Consent mode and cookie consent management apps like Cookiebot.

https://support.cookiebot.com/hc/en-us/articles/360009192739-Google-Tag-Manager-and-Automatic-cookie-blocking

[vanska]

@aileenrose If still relevant, I made a plugin for Cookiebot that does just this https://github.com/nitrofi/gatsby-plugin-cookiebot