update billing API docs for public preview

[tlotemporal]

Temporal Affiliation

* [x] I am a Temporal employee

Page URL

https://docs.temporal.io/cloud/billing-api

Content Issue

Update to Public Preview on Thursday, May 14.

Update:

Report data limitations
For pre-release, reports can be generated with hourly granularity only, for the current billing month, and the previous billing month.

To:

Report data limitations
Reports can be generated with hourly, daily and monthly granularity.
Hourly for the current billing month, and the previous billing month.
Daily for the current billing month, and previous three billing months.
Monthly for the current billing month, and previous twelve billing months

[jsundai]

PR 4557