Impose limit on the number of PII rules

[jjbayer]

Make sure that every part of PII config (legacy config like sensitive fields, but also / especially advanced data scrubbing rules) are limited, to prevent excessive project config sizes and Relay CPU usage.

• [ ] What is the maximum amount of rules / longest regex that customers have in place currently? Use redash to figure this out.
• [ ] Impose a sentry-side limit on each field (e.g. 100).

Internal case: https://www.notion.so/sentry/f229f90a26c24bc7a4d565741784c490