ExceptionlessTarget - ApiKey and ServerUrl and Message and UserIdentity with Layout support

[snakefoot]

Resolves #297 and resolves #296

    <target type="Exceptionless, Exceptionless.NLog" name="exceptionless"
            apiKey="API_KEY_HERE"
            userIdentity="${aspnet-user-identity}"
            userIdentityName="${aspnet-user-claim:ClaimTypes.Name}">
      <field name="host" layout="${hostname}" />
      <field name="process" layout="${processname}" />
      <field name="user" layout="${environment-user}" />
    </target>

${aspnet-user-identity} comes from NLog.Web.AspNetCore-nuget-package . See also: https://nlog-project.org/config/?tab=layout-renderers

[CLAassistant]

All committers have signed the CLA.

[niemyjski]

I left a comment. I don't think we can use reference id's like this because they will be discarded events server side as each event needs to be unique, can you please confirm.

[niemyjski]

I left a comment. I don't think we can use reference id's like this because they will be discarded events server side as each event needs to be unique, can you please confirm.

@ejsmith may want to consider bringing correlation id in as it may help track down issues in otel. I'm not sure how well our event references we store in extended data for this scenario would help.

[niemyjski]

Looks great, had a question about target changes

[niemyjski]

Thanks for the PR!!!!!!