Ensure storage rule is removed if lets encrypt process fails

[marrobi]

Description
The lets encrypt script adds and then removes storage account access rule with the client IP. If the script fails then the firewall rule with client IP remains. This should not be the case.

[marrobi]

@jonnyry can your script in this PR, resolve this too?

#4260

[jonnyry]

@marrobi The script in PR #4260 is specifically for the key vault, but if we followed the same pattern for the storage account, it would resolve this ticket.

Essentially uses a Bash exit trap to hook the end of the script execution, which fires whether an error occurs or not.

Could parameterise the storage account like sa_add_network_exception.sh --storage-account-name stwebmytre so it can be used in different scenarios.

[marrobi]

Please use the same method as in ./devops/scripts/mgmtstorage_enable_public_access.sh . Open the static web storage to all addresses, rather than a specific address. this also removes the need for LETSENCRYPT_DROP_ALL_RULES