RFR: 1660: Add confname field to slack log config

[Zhao Song]

On Wed, 2 Nov 2022 20:40:04 GMT, Erik Joelsson <erikj at openjdk.org> wrote:

> The Slack log handler currently takes a "username" value as input which if set is sent to Slack as the user name of the message. With modern webhooks, it unfortunately seems that we have lost the feature of overriding the user name of a message. Our current configs put a descriptive string identifying the bot configuration in this field, which we can no longer see.
> 
> I want to add a specific new configuration field to the Slack log handler for the "configname". If set, this will appear first in every Slack message.

LGTM

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Marked as reviewed by zsong (Author).

PR: https://git.openjdk.org/skara/pull/1413