Improve frontend runtime error monitoring with Sentry

[taylorsperry]

Problem to solve

Today, we lack processes around client-side monitoring errors, error reporting, and prioritizing and fixing runtime errors. Consequently:

• The cloud instance can be inaccessible for a significant amount of time without anyone noticing
• Even when problems are observed, it's unclear where to report and track the issue
• Issues are ignored when ownership areas are unclear
• Errors are swallowed that shouldn't be

Measure of success

Solution summary

Artifacts:

• RFC 501 REVIEW: Runtime error monitoring

What specific customers are we iterating on the problem and solution with?

Internal Sourcegraph developers

Impact on use cases

Delivery plan

• TO DO

[valerybugakov]

We have a tracking issue for this RFC here. Probably we should close one as a duplicate or update the description to communicate the difference.

[taylorsperry]

Good point, @valerybugakov. I updated the existing issue to incorporate the format of the roadmap issues and am closing this one. Hopefully this will help streamline things.