Make a postprocess script that update AWS_metadata.csv

[BaptisteVandecrux]

In that file, we should update:

• last valid timestamp (looking at a subset of key variables: t_u, p_u...)
• timestamp of last known coordinates (can be sometimes years prior to the last valid time stamp)
• last known latitude, longitude, elevation

Optional:

• also look at the first 1-2 week of data and re-estimate the coordinates of AWS at installation, which might evolve as further QC cleans the GPS data. This step could also been done manually after major QC updates.

[BaptisteVandecrux]

done in #294