EventHub: Revert removing of messaging plan and updated with examples

[v-Ajnava]

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Automation for azure-sdk-for-python

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Azure/azure-sdk-for-python#2051

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[v-Ajnava]

@sarangan12 , previous PR (#2831) where @hovsepm provided review comments which are addressed here.
previous PR was closed to address revert removing messaging plan commit.

ARM approval for MessagningPlan is in #2457

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Automation for azure-sdk-for-node

The initial PR has been merged into your service PR:
Azure/azure-sdk-for-node#2658

[hovsepm]

this is rework of the PR #2831

[hovsepm]

@sarangan12 I'll take care of this one since I have more context through email communication.

[jhendrixMSFT]

@AutorestCI regenerate azure-sdk-for-go