UI for actions is not pluggable

[johnaohara]

Describe the bug

The UI for actions is not pluggable, so every new action needs explicitly adding to the UI:

https://github.com/Hyperfoil/Horreum/blob/master/horreum-web/src/domain/actions/ActionComponentForm.tsx#L111

This does not scale as an architecture as more actions are added

We need a pluggable architecture, similar to the change detection implementations:

https://github.com/Hyperfoil/Horreum/blob/master/horreum-backend/src/main/java/io/hyperfoil/tools/horreum/changedetection/FixedThresholdModel.java#L20

https://github.com/Hyperfoil/Horreum/blob/master/horreum-web/src/domain/tests/VariableForm.tsx#L226