SpringBoot Add support for Micrometer tracing

Implements auto-configurations for Micrometer Tracing

See gh-30156

So far this auto-configuration supports:

• Zipkin with a configurable URL, using JSON_V2 encoding and HTTP transport
• Wavefront with a configurable URL
• Configurable sampling probability (0% - 100%) for Brave and for OpenTelemetry
• Brave configured for Zipkin
• Brave propagation with B3 headers
• OpenTelemetry configured for Zipkin
• Micrometer tracing bridges for Brave and OpenTelemetry
• Micrometer observation handler for tracing
• Brave configured for Wavefront
• OpenTelemetry configured for Wavefront

Comment From: mhalbritter

These are the dependency combinations i have tested with and which produce spans in backends:

Zipkin & Brave (no spring-web)

    implementation 'org.springframework.boot:spring-boot-starter-actuator'
    implementation 'io.micrometer:micrometer-tracing-bridge-brave'
    implementation 'io.zipkin.reporter2:zipkin-sender-urlconnection'


Zipkin & Brave (RestTemplate)

    implementation 'org.springframework.boot:spring-boot-starter-actuator'  
    implementation 'io.micrometer:micrometer-tracing-bridge-brave'
    implementation 'org.springframework.boot:spring-boot-starter-web'

Zipkin & Otel (no spring-web)

    implementation 'org.springframework.boot:spring-boot-starter-actuator'
    implementation 'io.micrometer:micrometer-tracing-bridge-otel'
    implementation 'io.zipkin.reporter2:zipkin-sender-urlconnection'
    implementation 'io.opentelemetry:opentelemetry-exporter-zipkin'

Zipkin & Otel (RestTemplate)

    implementation 'org.springframework.boot:spring-boot-starter-actuator'
    implementation 'io.micrometer:micrometer-tracing-bridge-otel'
    implementation 'org.springframework.boot:spring-boot-starter-web'
    implementation 'io.opentelemetry:opentelemetry-exporter-zipkin'

Wavefront & Otel

    implementation 'org.springframework.boot:spring-boot-starter-actuator'
    implementation 'io.micrometer:micrometer-tracing-bridge-otel'
    implementation 'io.micrometer:micrometer-tracing-reporter-wavefront'

Wavefront & Brave

    implementation 'org.springframework.boot:spring-boot-starter-actuator'
    implementation 'io.micrometer:micrometer-tracing-bridge-brave'
    implementation 'io.micrometer:micrometer-tracing-reporter-wavefront'

For Wavefront, at least the management.wavefront.api-token must be set, otherwise startup fails:

Caused by: org.springframework.boot.context.properties.source.InvalidConfigurationPropertyValueException: Property management.wavefront.api-token with value 'null' is invalid: This property is mandatory whenever publishing directly to the Wavefront API
    at org.springframework.boot.actuate.autoconfigure.wavefront.WavefrontProperties.getApiTokenOrThrow(WavefrontProperties.java:125) ~[classes/:na]
    at org.springframework.boot.actuate.autoconfigure.wavefront.WavefrontAutoConfiguration.wavefrontSender(WavefrontAutoConfiguration.java:51) ~[classes/:na]
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:na]
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:77) ~[na:na]
    at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:na]
    at java.base/java.lang.reflect.Method.invoke(Method.java:568) ~[na:na]
    at org.springframework.beans.factory.support.SimpleInstantiationStrategy.instantiate(SimpleInstantiationStrategy.java:130) ~[spring-beans-6.0.0-M3.jar:6.0.0-M3]
    ... 140 common frames omitted

Comment From: mhalbritter

Blocked on https://github.com/micrometer-metrics/tracing/issues/16

Comment From: mhalbritter

Rebased and put into main, see https://github.com/spring-projects/spring-boot/commit/3860eb211af1b429f325c05408ba2ebc82ae6698