Refactor the agent.yaml configuration file #21067

[jiangML]

Fixes #21067.

Changes proposed in this pull request:

• Refactor: refactor the agent.yaml configuration file
• Adjust the format of the agent.yaml configuration parameter
• Update observability documentation

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Before committing this PR, I'm sure that I have checked the following options:

• [x] My code follows the code of conduct of this project.
• [x] I have self-reviewed the commit code.
• [x] I have triggered maven check: mvn clean install -B -T2C -DskipTests -Dmaven.javadoc.skip=true -e.
• [x] I have made corresponding changes to the documentation.
• [x] I have added corresponding unit tests for my changes.

[codecov-commenter]

Codecov Report

Merging #21118 (a4bf302) into master (ba081e0) will decrease coverage by 0.01%. The diff coverage is 35.71%.

@@             Coverage Diff              @@
##             master   #21118      +/-   ##
============================================
- Coverage     61.72%   61.70%   -0.02%     
  Complexity     2543     2543              
============================================
  Files          4069     4070       +1     
  Lines         56173    56188      +15     
  Branches       9471     7489    -1982     
============================================
+ Hits          34670    34673       +3     
+ Misses        18610    18576      -34     
- Partials       2893     2939      +46     

Impacted Files	Coverage Δ
...agent/core/config/yaml/YamlAgentConfiguration.java	0.00% <ø> (ø)
...e/config/yaml/YamlPluginCategoryConfiguration.java	0.00% <0.00%> (ø)
...ig/yaml/swapper/YamlAgentConfigurationSwapper.java	0.00% <0.00%> (ø)
...ingsphere/agent/core/plugin/AgentPluginLoader.java	0.00% <0.00%> (ø)
...re/agent/core/plugin/PluginBootServiceManager.java	0.00% <ø> (ø)
...definition/BaseLoggingPluginDefinitionService.java	0.00% <0.00%> (ø)
...ing/base/service/BaseLoggingPluginBootService.java	0.00% <0.00%> (ø)
...jaeger/service/JaegerTracingPluginBootService.java	73.68% <80.00%> (+7.01%)	:arrow_up:
...agent/metrics/api/advice/SQLRouteEngineAdvice.java	92.85% <100.00%> (ø)
...rometheus/service/PrometheusPluginBootService.java	68.00% <100.00%> (-4.00%)	:arrow_down:
... and 34 more

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