Add description in azure-eventgrid to tell users to use azure-messaging-eventgrid

[YijunXieMS]

closes #22135

azure-eventgrid isn't in version_client.txt so there is no need to update there.
The last azure-eventgrid version on maven is 1.4.0-beta.1 (https://mvnrepository.com/artifact/com.microsoft.azure/azure-eventgrid). So this PR uses 1.4.0-beta.2.

[ramya-rao-a]

The last azure-eventgrid version on maven is 1.4.0-beta.1 (https://mvnrepository.com/artifact/com.microsoft.azure/azure-eventgrid). So this PR uses 1.4.0-beta.2.

We will soon be marking this package as deprecated. So it does not make sense to me to continue using the beta nomenclature. Can we get details from the package owners on what features were in beta in the last version and whether there are plans to ever make them GA?

I would recommend the following options

• If the beta features are not meant to go GA, then either remove them and ship 1.4.0 or do a 1.3.1
• If the beta features are meant to go GA, then do a direct 1.4.0

[YijunXieMS]

The last azure-eventgrid version on maven is 1.4.0-beta.1 (https://mvnrepository.com/artifact/com.microsoft.azure/azure-eventgrid). So this PR uses 1.4.0-beta.2.

We will soon be marking this package as deprecated. So it does not make sense to me to continue using the beta nomenclature. Can we get details from the package owners on what features were in beta in the last version and whether there are plans to ever make them GA?

I would recommend the following options

• If the beta features are not meant to go GA, then either remove them and ship 1.4.0 or do a 1.3.1
• If the beta features are meant to go GA, then do a direct 1.4.0

The repo doesn't have a tag/release for the last GA version 1.2.0. Will need to use a tool to compare the current code in repo vs 1.2.0 source code to see if there is any risk. Will update this PR if the current code is good for GA.