add info about custom latency buckets

[filintod]

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Description

Information about new customization of latency buckets.

Depends on https://github.com/dapr/dapr/pull/7843

Issue reference

https://github.com/dapr/dapr/issues/7641

[filintod]

@alicejgibbons

[msfussell]

@filintod - Taking a look today