Add and enable blackbox_exporter package

*blackbox_exporter* is a generic exporter for Prometheus that can be
used to provide metrics about HTTP, etc. services.  I use it to monitor
the availability and responsiveness of websites I host.

Config.in

@@ -1,3 +1,4 @@
 source "$BR2_EXTERNAL_metricspi_PATH/package/alertmanager/Config.in"
+source "$BR2_EXTERNAL_metricspi_PATH/package/blackbox_exporter/Config.in"
 source "$BR2_EXTERNAL_metricspi_PATH/package/grafana/Config.in"
 source "$BR2_EXTERNAL_metricspi_PATH/package/victoriametrics/Config.in"

configs/metricspi_defconfig

@@ -110,6 +110,7 @@ BR2_TARGET_ROOTFS_SQUASHFS=y
 BR2_TARGET_ROOTFS_SQUASHFS4_XZ=y
 # BR2_TARGET_ROOTFS_TAR is not set
 BR2_PACKAGE_ALERTMANAGER=y
+BR2_PACKAGE_BLACKBOX_EXPORTER=y
 BR2_PACKAGE_GRAFANA=y
 BR2_PACKAGE_VICTORIAMETRICS=y
 BR2_PACKAGE_VICTORIAMETRICS_SINGLE=y

package/blackbox_exporter/Config.in

@@ -0,0 +1,4 @@
+config BR2_PACKAGE_BLACKBOX_EXPORTER
+	bool "blackbox_exporter"
+	help
+	  Prometheus Blackbox Exporter

package/blackbox_exporter/blackbox_exporter.mk

@@ -0,0 +1,20 @@
+###############################################################################
+#
+# Prometheus Blackbox Exporter
+#
+###############################################################################
+
+BLACKBOX_EXPORTER_VERSION = 0.22.0
+BLACKBOX_EXPORTER_SITE = $(call github,prometheus,blackbox_exporter,v$(BLACKBOX_EXPORTER_VERSION))
+BLACKBOX_EXPORTER_LICENSE = Apache-2.0
+BLACKBOX_EXPORTER_LICENSE_FILES = LICENSE
+
+BLACKBOX_EXPORTER_LDFLAGS = -extldflags '-static'
+
+define BLACKBOX_EXPORTER_INSTALL_INIT_SYSTEMD
+	$(INSTALL) -D -m u=rw,go=r \
+		$(BR2_EXTERNAL_metricspi_PATH)/package/blackbox_exporter/blackbox_exporter.service \
+		$(TARGET_DIR)/usr/lib/systemd/system/blackbox_exporter.service
+endef
+
+$(eval $(golang-package))

package/blackbox_exporter/blackbox_exporter.service

@@ -0,0 +1,45 @@
+[Unit]
+Description=Blackbox exporter
+Documentation=https://github.com/prometheus/blackbox_exporter/blob/master/README.md
+After=network-online.target
+Wants=network-online.target
+
+[Service]
+Type=exec
+ExecStart=/usr/bin/blackbox_exporter \
+	--config.file=/etc/prometheus/blackbox.yml \
+	--web.listen-address=[::1]:9115
+ExecReload=/bin/kill -HUP $MAINPID
+Restart=on-failure
+
+CapabilityBoundingSet=
+DeviceAllow=
+DevicePolicy=closed
+DynamicUser=yes
+LockPersonality=yes
+MemoryDenyWriteExecute=yes
+NoNewPrivileges=yes
+PrivateDevices=yes
+PrivateUsers=yes
+PrivateTmp=yes
+ProcSubset=pid
+ProtectClock=yes
+ProtectControlGroups=yes
+ProtectHome=yes
+ProtectHostname=yes
+ProtectKernelLogs=yes
+ProtectKernelModules=yes
+ProtectKernelTunables=yes
+ProtectProc=invisible
+ProtectSystem=strict
+RestrictAddressFamilies=AF_INET AF_INET6
+RestrictNamespaces=yes
+RestrictRealtime=yes
+RestrictSUIDSGID=yes
+SystemCallArchitectures=native
+SystemCallFilter=@system-service
+SystemCallFilter=~@privileged @resources
+UMask=0027
+
+[Install]
+WantedBy=multi-user.target