Add sample data for Uptime

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We should provide sample data for Uptime to improve the getting started experience.

There is a broader initiative (see: elastic/kibana#40704) to provide sample data for all Observability solutions. We should do this to ensure we have parity with the experience provided by the other Obs. teams.

This would involve the generation of sample data. Ideally, we would integrate our sample data with values provided by the other solutions, so that users importing it for one solution will be able to leverage the integrations we maintain across solutions.