Note fire-and-forget status of HubConnection event tasks

[Smaug123]

Document fire-and-forget status of HubConnection event tasks

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Document the fate of the Tasks associated with HubConnection events.

Description

Verification:

• Reconnecting
• Closed
• Reconnected.

Fixes #57777 .

[dotnet-policy-service]

Thanks for your PR, @Smaug123. Someone from the team will get assigned to your PR shortly and we'll get it reviewed.

[dotnet-policy-service]

Looks like this PR hasn't been active for some time and the codebase could have been changed in the meantime.
To make sure no conflicting changes have occurred, please rerun validation before merging. You can do this by leaving an /azp run comment here (requires commit rights), or by simply closing and reopening.