Disable matrix-matrixto for Watchtower

[der-domi]

This solves #4820.

• Add the additional label for Matrix.to to disable to disable Watchtower's notification.

[spantaleev]

This works, but.. matrix_matrixto_container_labels_additional_labels is meant to be used by people to inject additional labels. If they start using this new variable, they will find that this special label is no longer being applied.

It's better to use something else - perhaps even a special matrix_matrixto_container_labels_watchtower_skip_enabled: true value which injects the correct label (perhaps the label can be configurable too, via matrix_matrixto_container_labels_watchtower_skip_label: com.centurylinklabs.watchtower.enable=false).

This frees up matrix_matrixto_container_labels_additional_labels for usage by others.

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An alternative is to split matrix_matrixto_container_labels_additional_labels into matrix_matrixto_container_labels_additional_labels_default, matrix_matrixto_container_labels_additional_labels_auto and matrix_matrixto_container_labels_additional_labels_custom. We have never done this for the "additional labels", but at least it's consistent with what we do with other variables.

These variables can then be merged into matrix_matrixto_container_labels_additional_labels, which will be used in the labels.j2 file as it currently is.

The watchtower-related label can be injected into matrix_matrixto_container_labels_additional_labels_default. Perhaps it should be conditional, via other variables (perhaps matrix_matrixto_container_labels_watchtower_skip_enabled and matrix_matrixto_container_labels_watchtower_skip_label).

[luixxiul]

An alternative is to split ...

Off-topic, but probably *_container_extra_arguments_auto, _default, _custom too? Some have already these, but not all do.

[spantaleev]

These could also work, but it's better to have the labels in the dedicated labels file, instead of dirtying up the systemd service file and making the container start command more complicated.

[der-domi]

Okay, thanks for the feedback. I will have a deeper look to it. But I need a while...