production/vault: Use a connection_string for the vault

It's required for the vault v1.9.2.

And matches what has been done for the staging vault.

octo-diff vangogh

diff origin/production/vangogh.euwest.azure.internal.softwareheritage.org current/vangogh.euwest.azure.internal.softwareheritage.org
*******************************************
  File[/etc/softwareheritage/vault/server.yml] =>
   parameters =>
     content =>
      @@ -95,7 +95,7 @@
       cache:
         cls: azure
      -  account_name: swh::azure::credentials::vaultstorage::account
      -  api_secret_key: swh::azure::credentials::vaultstorage::key
      -  container_name: contents
      +  connection_string: DefaultEndpointsProtocol=https;AccountName=swh::azure::credentials::vaultstorage::account;AccountKey=swh::azure::credentials::vaultstorage::key;EndpointSuffix=core.windows.net
      +  container_name: contents-uncompressed
      +  compression: none
       smtp:
         host: localhost
*******************************************
*** End octocatalog-diff on vangogh.euwest.azure.internal.softwareheritage.org

Refs. swh/infra/sysadm-environment#5103 (closed)