Add metrics collection exercises

[calebhailey]

Suggested Improvement

Metrics collection exercises are currently marked as "todo" in lessons 4 and 8. Let's add examples for each reference architecture (influxdb, sumologic, elasticsearch, prometheus, etc).

Applicable Lessons

• [ ] Lesson 01 completed or in-progress
• [ ] Lesson 02 completed or in-progress
• [ ] Lesson 03 completed or in-progress
• [x] Lesson 04 completed or in-progress
• [ ] Lesson 05 completed or in-progress
• [ ] Lesson 06 completed or in-progress
• [ ] Lesson 07 completed or in-progress
• [x] Lesson 08 completed or in-progress
• [ ] Lesson 09 completed or in-progress
• [ ] Lesson 10 completed or in-progress
• [ ] Lesson 11 completed or in-progress
• [ ] Lesson 12 completed or in-progress
• [ ] Lesson 13 completed or in-progress
• [ ] Lesson 14 completed or in-progress
• [ ] Lesson 15 completed or in-progress
• [ ] Lesson 16 completed or in-progress