Add server creation parameters to Postgres ResourceProvider for SDK

[grigusev]

This PR is a request to merge, the change was already reviewed in https://github.com/Azure/azure-rest-api-specs-pr/pull/574/

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[msftclas]

All CLA requirements met.

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[sarangan12]

Already reviewed, approved and merged in https://github.com/Azure/azure-rest-api-specs-pr/pull/574/files. Approving and merging it now.