update slack-notifier to 1.0.0, use raw webhook_url per slack recommendation

per changes with slack, they’re now using “static” web hook urls that describe the team & service with IDs that don’t change if the team or service name change. their recommendation is to use the raw webhook_url instead of building it out of components to allow more flexibility

this should also prevent issues cropping up with mistakes in how the urls are parsed
Merge pull request #8156 from stevenosloan/update_slack_and_use_raw_webhook_url

update slack-notifier for new webhook_url format