Review .updated.json usage

[ben-polinsky]

When building and publishing our documentation, we keep a running map of when pages were last updated. To do this, we keep a map of pages->time last updated, publishing it as a build artifact for consumption by the next documentation CI build.

This has mostly worked, but a couple issues have surfaced:

1. The last updated times do not always match the file's commit history. For instance, see this page: https://www.itwinjs.org/learning/geolocation/ - the last updated time is 15 May, 2024 yet commit history shows the file hasn't been touched in years

2. When creating new release branches, we must remember to update the download task branch after an artifact is published from that build. For example, in creating a new branch release/10.x we initially point the branch to release/9.x as that's the most recently published branch. Then, after one run of release/10.x which publishes an updated artifact, we can change the branch to release/10.x. Remembering to do this is error-prone.

@DanRod1999