feat(metric): Add prometheus pushgateway support

[FoghostCn]

1. removed metrics configurations:
   • Mode: only supports pull mode before,now use prometheus.exporter.enabled and prometheus.pushgateway.enabled instead, and pull mode is the default behavior if metrics.enable is true
   • Namespace: does not support modification. it is useless now
   • PushGatewayAddress: never supported before. prometheus.pushgateway.* is the new config
2. removed file:
   • common/extension/metrics.go and common/extension/metrics_test.go, since metric extension way is changed,they are useless now. see refactor: rewrite RPC metrics into the event pattern #2392 for more information .
   • metrics/prometheus/reporter.go,move export method to metricRegistry.export
3. Add prometheus pushgateway support, we can enabled it by config:

  metrics:
    prometheus:
      pushgateway:
        enabled: true
        base-url: "localhost:9999"
        job: myjob
        username: dubbo
        password: 1234
        push-interval: 10

[sonarqubecloud]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
2 Code Smells

No Coverage information
0.0% Duplication

[codecov-commenter]

Codecov Report

Merging #2415 (a640f4c) into main (da40230) will increase coverage by 0.68%.
The diff coverage is 48.57%.

❗ Current head a640f4c differs from pull request most recent head 5df3bc3. Consider uploading reports for the commit 5df3bc3 to get more accurate results

@@            Coverage Diff             @@
##             main    #2415      +/-   ##
==========================================
+ Coverage   44.37%   45.06%   +0.68%     
==========================================
  Files         303      269      -34     
  Lines       18411    18157     -254     
==========================================
+ Hits         8170     8182      +12     
+ Misses       9377     9105     -272     
- Partials      864      870       +6     

Files Changed	Coverage Δ
config/metric_config.go	52.17% <0.00%> (-17.60%)	⬇️
metrics/prometheus/registry.go	77.77% <62.96%> (-11.42%)	⬇️

... and 32 files with indirect coverage changes

📣 We’re building smart automated test selection to slash your CI/CD build times. Learn more

[ev1lQuark]

Nice work! LGTM.