preparations for soft deprecation of legacy notification args

[piksel]

this PR contains initial work for an eventual soft deprecation of legacy notification args.
the main feature added is the notify-upgrade command that can be used as an easy upgrade path for users that currently rely on the legacy notification wrappers.

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (main@2102a05). Click here to learn what that means.
Patch coverage: 84.61% of modified lines in pull request are covered.

❗ Current head 9250ada differs from pull request most recent head 733c37b. Consider uploading reports for the commit 733c37b to get more accurate results

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1377   +/-   ##
=======================================
  Coverage        ?   64.76%           
=======================================
  Files           ?       24           
  Lines           ?     2310           
  Branches        ?        0           
=======================================
  Hits            ?     1496           
  Misses          ?      718           
  Partials        ?       96           

Impacted Files	Coverage Δ
pkg/container/container.go	50.58% <ø> (ø)
pkg/container/cgroup_id.go	50.00% <50.00%> (ø)
pkg/notifications/shoutrrr.go	74.46% <85.71%> (ø)
pkg/notifications/email.go	93.87% <100.00%> (ø)
pkg/notifications/gotify.go	71.11% <100.00%> (ø)
pkg/notifications/msteams.go	66.66% <100.00%> (ø)
pkg/notifications/notifier.go	87.25% <100.00%> (ø)
pkg/notifications/slack.go	94.33% <100.00%> (ø)

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