Metadata querying: specify the arrow of time for Last-Modified queries

[Xe]

While I was on stream, I was confused at the "directionality" of time in X-Tigris-Query calls. Specifically, I wanted to get objects that were a week older or more. The example shows this:

`Last-Modified` > "2024-06-23T10:38:46Z"

I wasn't sure if this meant everything before or after the given point in time. I now understand that to get what I want, I needed to do code like this:

t := time.Now().AddDate(0, 0, -7)
aWeekAgo := t.Format(time.RFC3339)
q := fmt.Sprintf("`Content-Type` = \"application/vnd.docker.distribution.manifest.v2+json\" AND `Last-Modified` < %q", aWeekAgo)

Document this and the "arrow of time".