builds.sr.ht/worker d---------
worker: fix controlcmd with spaces
Implement CI_NAME=sourcehut

This commit pushes a new environment variable, `CI_NAME' which can be
used to reliably detect if some code is running under builds.sr.ht
worker: update gocelery and fix shutdown procedure
worker: populate job owner in webhook payload
worker: sign webhook payload
Add `oauth` option to manifest

Which creates an OAuth2 bearer token for the submitter on the fly, only
if secrets are enabled.
worker: improve webhook failure handling

Logs the error to the build log and increments a Prometheus counter for
later reference.
worker: correct error with job groups of mixed tags
Initial support for job group triggers
Initial support for job groups
worker: trim wc output before splitting it

Apparently OpenBSD indents the output of wc; see
worker: omit tasks from email if they begin with _
Expand capabilities of the email trigger

Adds In-Reply-To and Cc options, and fixes multiple recipients
worker: handle nil environment values
Plan 9: use git/branch to check out commits
worker: fix error with cloning several repos
worker/context: drop -G from drawterm
worker: generalize hacks for Plan 9 support
Initial pass on Plan 9 support
artifacts: show better error message on ~/example