Rename SMTPS to Submissions and deprecate old variable

[WebSpider]

Fixes #364

[github-actions]

This PR is stale because it has been open 45 days with no activity. Remove stale label or comment or this will be closed in 10 days.

[WebSpider]

Well, its ready for merge, so it would be appreciated not to close it.

[github-actions]

This PR is stale because it has been open 45 days with no activity. Remove stale label or comment or this will be closed in 10 days.

[WebSpider]

Unstale once more

[WebSpider]

@fastlorenzo i dont mind helping out with maintenance of these charts. Let me know how i can help.

[aki-ks]

I think before this get's merged and released, a hint could be inserted that, if the old variable is used, the chart fails to render, spitting an explanatory error, that tells about the deprecation. This breaking change would e.g. break my mailu deployment if I would upgrade.

---

Here's an example what traefik did, when they made a breaking change to theirs values schema:
https://github.com/traefik/traefik-helm-chart/blob/39a4a3d66b28b11b8bec0f0dc2fb53712b9716df/traefik/templates/_podtemplate.tpl#L605-L607

Their previous syntax was:

ports:
  web:
    redirectTo: websecure

This was changed to the following:

ports:
  web:
     redirections:
        entryPoint:
          to: websecure
          scheme: https
          permanent: true

When the old Syntax is used today, the Chart fails to render and yields an explanatory error