Add missing unit of measure to IConfigurationReader.cs (1.27.0)

[monty241]

See IConfigurationReader.cs of Elastic APM for .net (1.27.0). The following properties lack a unit of measure such as minute, millisecond, tick or whatever:

• ExitSpanMinDuration
• SpanCompressionExactMatchMaxDuration
• SpanCompressionSameKindMaxDuration