Allow additional properties in DashboardParameter

[michal-billtech]

📝 Description of the PR

Adds support for additional properties in DashboardParameter

[flovouin]

Hi @michal-billtech, thanks for this and sorry for the delay.
Do you expect to use more properties than what you included in the test?
If not, how about adding them as their own properties in the OpenAPI?

[michal-billtech]

I saw that you took a similar approach with CardParameter. It seemed to me more beneficial since there seems to be no schema validation messages passed to the user and thus no real benefit to explicitly defining the scheme. On the other hand doing it this way makes it less prone to schema updates on Metabase's side. Am I missing something? Or maybe you've plans to implement schema validation reporting?

[flovouin]

Thanks for the reply. To be fair I didn't remember this was a pattern I had already used. Let's merge it like this.