feat(feature-showcase): Redesign and rewrite FeatureTourModal as FeatureShowcase

[malwilley]

Ref ISWF-2160

We need to use a multi-step modal to demo the new Monitors/Alerts product, and we do already have FeatureTourModal which does that and is used in a few hard-to-find places. However, that modal is a bit outdated design-wise and doesn't have the most flexible API (and is a class component).

I decided to rewrite it, and to rename it FeatureShowcase (so that it will not be confused with the existing Tour compoent).

FeatureShowcase is a compound component, and the usage is like so (you can also see this in the story file):

openModal(deps => (
  <FeatureShowcase {...deps}>
    <FeatureShowcase.Step>
      <FeatureShowcase.Image src={image} alt="Step title" />
      <FeatureShowcase.StepTitle>Step title</FeatureShowcase.StepTitle>
      <FeatureShowcase.StepContent>Step description</FeatureShowcase.StepContent>
      <FeatureShowcase.StepActions />
    </FeatureShowcase.Step>
  </FeatureShowcase>
));

See Figma designs here (though I could not match precisely due to the default modal padding being quite large).

Before:

After:

[linear-code]

ISWF-2160 Monitors/Alerts onboarding flow

[saponifi3d]

🤔 should we decompose this PR into 2; 1 that creates the new modal prop and another that implements it? mostly just thinking of it as a way to reduce risk when merging / deploying. (also, not a huge deal to do since i was able to review it all)

[github-actions]

🚨 Warning: This pull request contains Frontend and Backend changes!

It's discouraged to make changes to Sentry's Frontend and Backend in a single pull request. The Frontend and Backend are not atomically deployed. If the changes are interdependent of each other, they must be separated into two pull requests and be made forward or backwards compatible, such that the Backend or Frontend can be safely deployed independently.

Have questions? Please ask in the #discuss-dev-infra channel.

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[malwilley]

@saponifi3d went ahead and updated this PR so that it only adds the new component, will open a followup PR with the rest.

[saponifi3d]

:woohoo: code looks good once the couple of failing tests are address 🙏