Remove or automate timestamp on esap-gui

Currently, the footer of https://sdc-dev.astron.nl/esap-gui bears the legend esap-gui version 21 jan 2022 - 10:00. There have been quite a few changes since 2022-01-21:

$ git diff --shortstat 'master@{2022-01-21}'
 33 files changed, 25564 insertions(+), 17502 deletions(-)

Further, I'm pretty sure that ESAP-GUI has been redeployed since then. A timestamp on the page that doesn't correspond to the version in use is not just inaccurate, it's actively confusing and unhelpful.

Minimum goal for this ticket: simply remove the timestamp, so it's not actually wrong.

Better: insert a timestamp (and/or as SHA1) corresponding to the actual git commit in use.