update to use /api/{projectId}/store

The default recommended rate limiting on the sentry
    documentation rate limits by `projectId`.

It's a better default to talk to a sentry server using the
    `/api/{projectId}/store` API.

This way multiple services talking to the same sentry
    server will not all get rate limited under the same
    projectId (which is presumably the empty string).
I reverted that change as it was a bikeshed :)