Documentation feedback: Clarify definitions of time range selector options

There does not appear to be documentation around the specifics behind some of the more generic time selector phrases like "Previous Week" - and they may behave differently than expected. Eg, does previous week start on Monday? Sunday? It appears this is also configurable. See this Slack thread for some details: https://raintank-corp.slack.com/archives/C025WTVRBSN/p1746226810824979 There may be others in the list, but the "week" one is the one that stands out likely the most confusing.