KTOR-3194 - enable customize default tags in micrometer

[LucasMilotich]

Subsystem Ktor-metrics-micrometer

Motivation Feature: https://youtrack.jetbrains.com/issue/KTOR-3194

Sometimes you need to override default tags and the only way was using this sentence in MicrometerMetrics installation: metrics.config().meterFilter(MeterFilter.ignoreTags($tag))

Solution I've created a default tags field which allows to be overwritten in the configuration class. Some fields/classes have to be internal in order to allow the client to access and customize tags using the call.