[web] Allow providing ReactNodes as Table header text

[kiosion]

Related to #5075. Allow providing ReactNodes as Table header text, e.g. so icons can be used as header text.

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[gzdunek]

I remember that some time ago I wanted to do something similar: allow string or ReactNode as notification content.

I found a comment from Rafał explaining why it was not the best idea:

I have to say I don't like this solution because it replicates the same problem that I mentioned when we were talking about using Markdown to insert the link: it shifts the responsibility of formatting the notification from the place which displays the notification to the place which wants the notification to be displayed.

If we add support for arbitrary HTML tags, if you want to answer the question of "How do all possible variants of notifications may look like, more or less?", you're no longer able to answer this question without grepping through all places in the codebase which add notifications because each one of them can do some custom stuff.

I think a better play here would be to add an optional link field to NotificationItemObjectContent. link could be an object with fields href and text. This way we support adding links to notifications while still making it possible to open a storybook and see all possible variants of notifications.

I think this applies here as well. Maybe we should instead add another prop, like:

headerIcon?: {
  Icon: React.ComponentType<IconProps>;
  ariaLabel: string // I assume we needed this for the icon?
}

[kiosion]

@gzdunek hmm, yeah, that makes sense to me, will try something along those lines instead.