Add more observability in apollo config client

[Anilople]

Is your feature request related to a problem? Please describe.
When use apollo config client, user want more observability,
for example,

• Ensure config dilivery success or not, what's actual config use in memory and which time they init, update
• What's the actual app.id, apollo.cluster, apollo.meta etc... use by JVM
• How many namespace use by current JVM, how many config item in a namespace
• Is network connection error when connect to apollo.meta?

But user cannot query above content directly

Describe the solution you'd like
First, we need to collect logs, metric, tracing as more as posible,
Then export them, by JMX, micrometer, dropwizard metrics or another framework.

Additional context
Current observability about apollo config client

• document https://www.apolloconfig.com/#/zh/design/apollo-design?id=_51-tracing
• code https://github.com/apolloconfig/apollo-java/blob/main/apollo-core/src/main/java/com/ctrip/framework/apollo/tracer/Tracer.java

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osapp https://summer-ospp.ac.cn/org/prodetail/24c4c0073

help document reference https://summer-ospp.ac.cn/help/student/

Any question can be post in this issue.

[nobodyiam]

This is very good proposal for production usage.

[shoothzj]

maybe we can use prometheus java client library https://github.com/prometheus/client_java