Update LinkedIn issuer.

[DovydasNavickas]

It seems that LinkedIn has updated their issuer:
https://www.linkedin.com/oauth/.well-known/openid-configuration

And now LinkedIn provider gives an error:

fail: OpenIddict.Client.OpenIddictClientDispatcher[0]
      An error occurred while retrieving the configuration of the remote authorization server.
      System.InvalidOperationException: IDX20803: Unable to obtain configuration from: 'https://www.linkedin.com/oauth/.well-known/openid-configuration'. Will retry at '8/15/2024 4:57:15 PM +00:00'. Exception: 'OpenIddict.Abstractions.OpenIddictExceptions+ProtocolException: An error occurred while handling the configuration response.
        Error: server_error
        Error description: The issuer returned in the server configuration doesn't match the value set in the client registration options.
        Error URI: https://documentation.openiddict.com/errors/ID2165
         at OpenIddict.Client.OpenIddictClientService.<>c__DisplayClass19_0.<<GetConfigurationAsync>g__HandleConfigurationResponseAsync|3>d.MoveNext()
      --- End of stack trace from previous location ---
         at OpenIddict.Client.OpenIddictClientService.GetConfigurationAsync(OpenIddictClientRegistration registration, Uri uri, CancellationToken cancellationToken)
         at OpenIddict.Client.OpenIddictClientService.GetConfigurationAsync(OpenIddictClientRegistration registration, Uri uri, CancellationToken cancellationToken)
         at OpenIddict.Client.OpenIddictClientRetriever.Microsoft.IdentityModel.Protocols.IConfigurationRetriever<OpenIddict.Abstractions.OpenIddictConfiguration>.GetConfigurationAsync(String address, IDocumentRetriever retriever, CancellationToken cancel)
         at Microsoft.IdentityModel.Protocols.ConfigurationManager`1.GetConfigurationAsync(CancellationToken cancel)'.
       ---> OpenIddict.Abstractions.OpenIddictExceptions+ProtocolException: An error occurred while handling the configuration response.
        Error: server_error
        Error description: The issuer returned in the server configuration doesn't match the value set in the client registration options.
        Error URI: https://documentation.openiddict.com/errors/ID2165
         at OpenIddict.Client.OpenIddictClientService.<>c__DisplayClass19_0.<<GetConfigurationAsync>g__HandleConfigurationResponseAsync|3>d.MoveNext()
      --- End of stack trace from previous location ---
         at OpenIddict.Client.OpenIddictClientService.GetConfigurationAsync(OpenIddictClientRegistration registration, Uri uri, CancellationToken cancellationToken)
         at OpenIddict.Client.OpenIddictClientService.GetConfigurationAsync(OpenIddictClientRegistration registration, Uri uri, CancellationToken cancellationToken)
         at OpenIddict.Client.OpenIddictClientRetriever.Microsoft.IdentityModel.Protocols.IConfigurationRetriever<OpenIddict.Abstractions.OpenIddictConfiguration>.GetConfigurationAsync(String address, IDocumentRetriever retriever, CancellationToken cancel)
         at Microsoft.IdentityModel.Protocols.ConfigurationManager`1.GetConfigurationAsync(CancellationToken cancel)
         --- End of inner exception stack trace ---
         at Microsoft.IdentityModel.Protocols.ConfigurationManager`1.GetConfigurationAsync(CancellationToken cancel)
         at OpenIddict.Client.OpenIddictClientHandlers.ResolveClientRegistrationFromChallengeContext.HandleAsync(ProcessChallengeContext context)

The most important line is:

The issuer returned in the server configuration doesn't match the value set in the client registration options.

If I understand correctly, the only update needed is the Issuer in OpenIddictClientWebIntegrationProviders.xml.

[kevinchalet]

Thanks for your PR, @DovydasNavickas ❤️

[kevinchalet]

Since LinkedIn now uses https://www.linkedin.com/oauth as the issuer, we can remove the ConfigurationEndpoint node 😃

[kevinchalet]

Merged, thanks for your contribution, @DovydasNavickas!

I'll backport it to the 5.7 branch and release a 5.7.1 version later today.