Separate exception for DNS errors

[mstojcevich-cisco]

Is your feature request related to a problem?

Currently the aiohttp client raises a ClientConnectorError when DNS resolution fails and there's no clean way to differentiate this ClientConnectorError from ones that happen at other points of the connection.

Describe the solution you'd like

I'd like another Exception, maybe ClientConnectorDNSError that inherits from ClientConnectorError and is raised when DNS resolution fails.

Describe alternatives you've considered

I've considered inspecting the ClientConnectorError to determine whether it's a DNS error, but it's tough to do so without making my calling code aware of the implementation details of the underlying DNS resolver.

Related component

Client

Additional context

No response

Code of Conduct

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