RFR: 1660: Add confname field to slack log config [v2]

[Erik Joelsson]

> 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.

Erik Joelsson has updated the pull request incrementally with one additional commit since the last revision:

  Change configname to prefix

-------------

Changes:
  - all: https://git.openjdk.org/skara/pull/1413/files
  - new: https://git.openjdk.org/skara/pull/1413/files/978e28aa..1da43017

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=skara&pr=1413&range=01
 - incr: https://webrevs.openjdk.org/?repo=skara&pr=1413&range=00-01

  Stats: 7 lines in 3 files changed: 0 ins; 0 del; 7 mod
  Patch: https://git.openjdk.org/skara/pull/1413.diff
  Fetch: git fetch https://git.openjdk.org/skara pull/1413/head:pull/1413

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