Update to OH 5.10.1 and a bunch of improvements (HEXA-1552)

[bramj]

• Update OpenHEXA to version 5.10.1
• Align the Debian package version with the OpenHEXA app/frontend version it ships. This to avoid confusion about the version numbering.
• Improved documentation for webapps Nginx config
• Add UPGRADING.md documenting per-version manual upgrade steps (new environment variables, breaking changes, migration commands). I chose to go this route instead of re-organizing .env.dist, I'd like to keep logical groupings there.
• Add openhexa.sh env-check [ENV_FILE] to diff your .env against .env.dist and report keys missing after an upgrade. ( runs automatically at the start of update, so the post-install hook warns about new variables without reading the docs)

  # example run
  $ ./script/openhexa.sh env-check .envlocal                                                                                                                                                                                              09:22:28
  Missing in your .envlocal (added in newer versions):
    ADDITIONAL_ALLOWED_HOSTS
    ALLOW_SELF_REGISTRATION
    ASSISTANT_MONTHLY_LIMIT
    DJANGO_SUPERUSER_EMAIL
    DJANGO_SUPERUSER_PASSWORD
    DJANGO_SUPERUSER_USERNAME
    FORGEJO_STORAGE_LOCATION
    GIT_SERVER_ADMIN_PASSWORD
    GIT_SERVER_ADMIN_USERNAME
    LOGFIRE_SEND_TO_LOGFIRE
    OAUTH2_ACCESS_TOKEN_EXPIRE_SECONDS
    OAUTH2_ALLOWED_REDIRECT_URI_HOSTS
    OVERRIDE_WORKSPACES_DATABASE_HOST
    STORAGE_BACKEND
    WEBAPPS_DOMAIN
    WORKSPACE_DATASETS_FILE_SNAPSHOT_SIZE
    WORKSPACE_STORAGE_BACKEND_AWS_ROLE_ARN
  
  Add the missing keys to .envlocal; the defaults are documented in .env.dist.
  Refer to the UPGRADING.md for guidance.

• Cleanup: remove unneeded ENV vars from .env.dist