Existing telemetry API's to survey

[tsloughter]

Here we can collect information on existing telemetry API's -- completely unrelated to OpenTelemetry or ones built on OpenTelemetry. How we want to use this information may require its own issue to discuss.

[tsloughter]

Micrometer has an API called Micrometer Observation which will create metrics and spans through the single API, https://docs.micrometer.io/tracing/reference/configuring.html

Example:

Observation.createNotStarted("my.operation", registry)
    .contextualName("This name is more readable - we can reuse it for e.g. spans")
    .lowCardinalityKeyValue("this.tag", "will end up as a meter tag and a span tag")
    .highCardinalityKeyValue("but.this.tag", "will end up as a span tag only")
    .observe(this::yourCodeToMeasure);

Gathered the following metrics
    Meter with name <my.operation> and type <TIMER> has the following measurements
        <[
            Measurement{statistic='COUNT', value=1.0},
            Measurement{statistic='TOTAL_TIME', value=1.011949454},
            Measurement{statistic='MAX', value=1.011949454}
        ]>
        and has the following tags <[tag(this.tag=will end up as a meter tag and a span tag)]>