Commit [958b41c4] added an event triggered when clicking on "Accept all" on a cookie banner (in 17.4) and [cee8a5e6] added support for Google Consent Mode V2 in master (18.0).
This commit backports the relevant parts of both so that stable versions are compliant with Google's policy and that the analytics are properly working. The event will also make it easier for customers to add custom code working with Odoo's standard cookie banner.

Note that due to [958b41c4], the behavior of Google Consent Mode is slightly different in stable versions than in 17.4 and above:
- In stable, Google is called on page load with consents set on denied. This grants that only cookieless pings, non-identifying information is sent to Google (see [Google's documentation]). It is updated once the cookies are accepted.
- In 17.4 and above, Google is not called until the cookies are accepted and only then receives the default + updated consents.

[958b41c4]: https://github.com/odoo/odoo/commit/958b41c4acec7e1700ca4d6e0b25ee0ad2aac9f1
[cee8a5e6]: https://github.com/odoo/odoo/commit/cee8a5e6aafd9c05e5b2c027e52aee6b174a4ad5
[Google's documentation]: https://support.google.com/google-ads/answer/10000067

Related to task-3880544

Forward-Port-Of: odoo/odoo#180866