Add ability to rate limit the number of attachments

[jjbayer]

Attachment quotas and rate limits are currently defined in bytes, so we have no way to prevent an abusively high number of very small attachments.

https://www.notion.so/sentry/Data-category-for-attachment-items-1518b10e4b5d80c8aec7fecaa0e53af6

Tasks

Preview Give feedback

1. feat(outcomes): Add data category for attachment item count #4374
   +0
2. Bump relay version in sentry and snuba
3. Enforce rate limits and report outcomes in relay
4. Define a project abuse limit (sentry side)

ref: INC-928 > IA-61

[jjbayer]

Bumping to P1 because it blocks resolution of INC-928.

[jjbayer]

We will add a new data category, but in relay internally experiment with the concept of a "unit".

https://www.notion.so/sentry/Data-category-for-attachment-items-1518b10e4b5d80c8aec7fecaa0e53af6