[Eventgrid] documentation issues

[rakshith91]

• Readme

• explain Difference between Event Grid events vs Cloud Events.
• update the sample of consuming event to include values
• add an example to send multiple events (batch events)
• Inconsistent terms in readme “hostname” and at portal “endpoint”, should be consistent

• Ref doc

• confusion in required vs optional in Event Grid and Cloud event schemas.
• data version is not marked as required
• “Cloud event doc id is optional, but “combination of source and id should be unique” was confusing [EventGrid] Small doc updates for id parameter #15835
• Topic is not listed as required in the ref doc for event grid domain
• Need better explanation on event schema parameters with examples of typical values

• Samples

• Explain/ add comments about env variables and how to add them - just add a stackoverflow issue about envars as an explanation

• Misc

• Make sure optional and non optional are well documented
• Document sending and receiving multistage decode of events better. try receiving a QueueEvent for instance and if documentation explains it. Also, give better explanation on Readme.