Update Event Hubs binding spec

[hhunter-ms]

What content needs to be created or modified?
Event Hubs binding spec needs updated to reflect that it now can read all message properties

Describe the solution you'd like
Add getAllMessageProperties to the spec metadata table and example
May need to add a section elsewhere in the doc

Where should the new material be placed?
Event Hubs binding spec

The associated pull request from dapr/dapr, dapr/components-contrib, or other Dapr code repos
dapr/components-contrib#3615