Disallow properties depending on itself

[barmac]

Describe the Bug

Right now, the schema allows a property to depend on itself. Specifically, the condition#property can take any value, and this can also be the id of the conditioned property. This leads to infinite loop which should be prevented via the JSON schema.

Steps to Reproduce

Check the conversation: https://camunda.slack.com/archives/C0693F1NFK5/p1704872988839289

Expected Behavior

Template should be rejected by the validator.

Environment

• Host (Browser/Node version), if applicable: [e.g. MS Edge 18, Chrome 69, Node 10 LTS]
• OS: [e.g. Windows 7]
• Library version: [e.g. 0.3.0]

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Discovered via https://camunda.slack.com/archives/C0693F1NFK5/p1704872988839289

[barmac]

We could also make sure that the condition#property value is one of the already existing property#ids.

[barmac]

We could use $data for this: https://json-schema.org/blog/posts/hyperborea#referencing-other-parts-of-the-schema

[barmac]

I experimented with $data, and this is the result: https://github.com/camunda/element-templates-json-schema/compare/main...125-disallow-properties-depending-on-itself?body=&expand=1

The solution works but requires to enable $data: true in the Ajv validator. The error message displayed in the editor is quite cryptic:

[barmac]

However, the cryptic error message can be adjusted thanks to the error-messages extension.

[barmac]

OK so actually the result from VSCode that I showed above is incorrect. VSCode does not handle $data as in ajv, so it doesn't matter whether we implement the constraint in the JSON schema or programmatically in the validator.

[barmac]

128 was reverted so this should be open again.