Allow multiple plug-ins to contribute lint rules and configuration

[nikku]

What is the Problem

There exists certain usage scenarios where, depending on different use-cases users ship different custom linter rules (cf. camunda/camunda-modeler-custom-linter-rules-plugin#5). Right now, it is not possible to inject such.

Describe the solution you'd like

• users may provide multiple "lint rule providing plug-ins"
• users can configure per diagram, which lint rules are being used

Additional Context

A potential UI sketch for how linting settings could be accessed:

[FO-e-X]

Merging different rules from different plugins should be easy to realize. But you mention the case for merging with default rules, the same for merging same rules in different plugins.
The simple case, each plugin provides independent rules and overrides different default rules or override them the same way. But merging the same (default) rules with different settings for each plugins sounds a bit tricky. This case I didn't thought about... Either the last loaded plugin wins the merging or, as your idea is, the user can choose via an UI.

[DoeMoor]

"Describe the solution you'd like"
-- users can configure per diagram, which lint rules are being used