Implement a comparison mode in climate monthly

[guidocioni]

It would be really cool to be able to have a comparison mode in climate monthly page where we compare the current year to the climatology.
We already have a code for that when we created figures like this

so we just need to implement it in the page.
I think the best way of doing this would be to have a toggle at the start of the page which activates this "comparison" mode, and in this case the first date range picker is maybe disabled (so that the default 1991-2020 is chosen) and the user can only select the year.
This is not extremely clean but I really don't want to create a new page just for this.