[sistent] Add Modal component to the sistent components page

[dragon-slayer875]

Current Behavior

Layer5 and it's projects use Sistent library to enable easy component reusability among our various projects.
One such component is Modal.

Ideally, all sistent components are represented on https://layer5.io/projects/sistent/components, but this component is currenly not.

Desired Behavior

Proper documentation for Modal component similar to Button component on https://layer5.io/projects/sistent/components
The documentation should include:

• Explanation about the various component props and their expected values
• Code examples for the various variants that a component might have (if any).

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