[Backup Service] Merge options are difficult to use from a user's perspective

Description:

The user may encounter the obstacle of deciphering what the 'Merge Offset Start' and 'Merge Offset End' mean.

For some context, here is what is shown to the user:

Merge Offset Start: 

Merge Offset End:

For a user to use the merge options correctly, the following ideas must be succesfully conveyed to them: 

• We're looking backwards in time.
• The end point is computed as today - merge_offset_start.
• The start point is computed as today - (merge_offset_start + merge_offset_end).
• The unit of merge_offset_start and merge_offset_end is in days.

A misunderstanding in any one of these areas may result in the user failing to configure the merge options correctly. 

For example:

• A user already familiar with cbbackupmgr may run into the mistake of thinking forwards in time.
• A user may compute the start point as today - merge_offset_end because it contains the word 'offset'.

A solution:

Instead, this POC diagram can express these ideas quite easily:

The diagram also reveals that the 'Merge End Offset' is more of a window or a size as opposed to an offset so perhaps a rename to 'Merge Window' or 'Merge Size' or 'Merge Window Size' instead may help.

(Side note: The arrow indicating time direction can be flipped with it's label changed to time flowing forwards in time)

(Side note: I should have also expressed the x axis is in days)