Add contextual help for range definition in page provider aggregates

Currently we do not give any clue about what to put inside a range: which keywords are available in a date range for instance. Goal is to provide user guidance on this.

AC
Ranges option shows contextual help depending on the type of aggregate

Range

Define the start and end numbers and associate a label to it. Leave the "from" or "to" field empty to accept any value. Some examples:

• under 1000: from [empty] to 1000
• between 1000 and 9000: from 1000.01 to 9000
• over 9000: from 9000.01 to [empty]

Date range

Define the start and end dates and associate a label to it. Leave the "from" or "to" field empty to accept any value. Some examples:

• past: from [empty] to now
• last year: from now-1y to now
• last month: from now-1M to now
• last week: from now-7d to now
• yesterday: from now-24h to now
• future: from now to [empty]