Add support for creating multiple replicated clusters in Bigtable hook and operator

[derrickqin]

Description

From Cloud Bigtable documentation

Cloud Bigtable supports up to 4 replicated clusters located in Google Cloud zones where Cloud Bigtable is available.
Currently Bigtable hook and operator only support creating one replicated cluster. It would be better to add support for creating multiple replicated clusters

Use case / motivation

Supporting multiple replicated clusters will be handy. It will be helpful to increase the availability and durability of the data by copying it across multiple regions or multiple zones within the same region.

[boring-cyborg]

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