Add events for upload start and end in cacholote

[malmans2]

Needs ecmwf-projects/cacholote#119

[FussyDuck]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you all sign our Contributor License Agreement before we can accept your contribution.
1 out of 2 committers have signed the CLA.

✅ malmans2
❌ francesconazzaro
_{You have signed the CLA already but the status is still pending? Let us recheck it.}