Merge branch '1.7.x' into 1.8.x

# Conflicts:
#	implementations/micrometer-registry-graphite/gradle.lockfile
#	implementations/micrometer-registry-statsd/gradle.lockfile
#	implementations/micrometer-registry-wavefront/gradle.lockfile
#	implementations/micrometer-registry-wavefront/src/test/java/io/micrometer/wavefront/WavefrontMeterRegistryTest.java
#	micrometer-core/gradle.lockfile
#	micrometer-test/gradle.lockfile
#	samples/micrometer-samples-boot2/gradle.lockfile
#	samples/micrometer-samples-core/gradle.lockfile