Add information about API limits for Invoke-AzOperationalInsightsQuery

[dcaro]

Description

We should add a note in the reference doc for Invoke-AzOperationalInsightsQuery cmdlet about the API rate limits:
https://docs.microsoft.com/en-us/azure/azure-monitor/service-limits#log-queries-and-language

[dingmeng-xue]

@VeryEarly , please look into this doc update.

[VeryEarly]

mentioned in doc: #13615

[dingmeng-xue]

Close it because doc is updated.