feat: support display of rule content that is not string

[jdromeiro]

Description

We want to be able to to support the display in the web UI of rule contents that are not strings.

For that purpose, the front-end was modified in order to correctly serialize and show RuleContent objects:

Note: if any property of the content is null, the UI will not display it.

Change checklist

• Code follows the code rules guidelines of this project
• Commit messages follow the commit rules of this project
• I have self-reviewed my changes before submitting this pull request
• I have covered new/changed code with new tests and/or adjusted existent ones
• I have made changes necessary to update the documentation accordingly

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