Support "months since" unit on NetCDF

Description

Although UCAR does not recommend using "months since DATE" unit since the resulting date may be very peculiar, there is some old data which still use it.
Panoply looks supporting them as made of 30 days.
We will use same approach

Environment

None

Status

Assignee

Daniele Romagnoli

Reporter

Daniele Romagnoli

Triage

None

Components

Fix versions

Priority

Medium
Configure