FreeBSD/ports a6b9524 (r512417). UPDATING, net-mgmt/pushgateway distinfo Makefile

Update to v0.9.1

Changelogs:
- https://github.com/prometheus/pushgateway/releases/tag/v0.9.1
- https://github.com/prometheus/pushgateway/releases/tag/v0.9.0
- https://github.com/prometheus/pushgateway/releases/tag/v0.7.0
- https://github.com/prometheus/pushgateway/releases/tag/v0.5.2
- https://github.com/prometheus/pushgateway/releases/tag/v0.5.1
- https://github.com/prometheus/pushgateway/releases/tag/v0.5.0
- https://github.com/prometheus/pushgateway/releases/tag/v0.4.0

The new persistent storage format is not backwards compatible. See the
changelogs for details.

- Define LICENSE_FILE.
- Switch to USES=go:modules
- Simplify targets.
- Fix a couple of typos and style issues in the service file
- Improve readability of comments in the service file
- Do not install /var/db/pushgateway by default. It is going to be created
  by the service anyway.

PR:             233660
Approved by:    maintainer
Event:          EuroBSDcon 2019 Hackathon
Differential Revision:  https://reviews.freebsd.org/D21729
DeltaFile
+23-25net-mgmt/pushgateway/files/pushgateway.in
+39-3net-mgmt/pushgateway/distinfo
+26-13net-mgmt/pushgateway/Makefile
+7-0UPDATING
+0-1net-mgmt/pushgateway/pkg-plist
+95-425 files

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