Updating the help_text for the SSH form

I updated the SSH form in order to create the `help_text` argument in
the form class and call it directly in the template.

Signed-off-by: Matthieu Berjon <matthieu.berjon@inria.fr>
1 job for 274-document-form-fields in 1 minute and 3 seconds (queued for 1 second)
Name Stage Failure
bootstrap Build
Step 7/7 : EXPOSE	25  143
---> Using cache
---> cacb460e7164
Successfully built cacb460e7164
Successfully tagged allgo_dev-smtpsink:latest
+ mkdir -p -- data/mysql
+ docker-compose run --rm dev-mysql sh -e -c 'if [ -f /dk/container_init ] ; then sleep 1; /dk/container_init ; fi'
error: db is already initialised
ERROR: Job failed: exit code 1