* Use <number>.<number> format for Google Analytics client ID
With the `ENFORCE_RECOMMENDATIONS` [validation behavior](https://developers.google.com/analytics/devguides/collection/protocol/ga4/validating-events?client_type=firebase#send_events_for_validation), Google Analytics warns about client IDs not in the <number>.<number> format.
This is not an issue in practice - that recommendation is for compatibility with existing client IDs and events are still processed with a client ID in any format. Additionally, the validation is not enabled by default.
However, this PR updates our sample code to use a consistent ID regardless to reduce noise if the validation is enabled. We use a random ID concatenated with a UNIX timestamp to match other GA client libraries.
* Run eslint
These were being loaded from a CDN from our old hosting
infrastructure for developer.chrome.com. This is no longer live,
and we shouldn't have been using external images anyway, so move
all of the images to the repo.
Fixes#1171
Updates a nunber of dependencies in a single PR. These were
suggested by dependabot but updating them individually would
mean the reposistory would be in a broken state until everything
had merged.
I'm not personally a huge fan of lowercasing doctype, but
Prettier has taken an opinionated stance here and there is not a
way to disable it:
https://github.com/prettier/prettier/issues/15096
