Add Arctic transects task to compare against ASTE reanalysis

[milenaveneziani]

It would be great to have vertical cross-sections of T, S, and cross-section velocities for Arctic transects, and compare them with Arctic Subpolar gyre sTate Estimate (ASTE) reanalysis data (https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2020MS002398), similarly to what done with SOSE transects.

Work to do:

• compute monthly climatologies from ASTE
• add a task taking the sose_transects task as reference

Some WIP can be found here (closed PR): #897