refactor: migrate old RT metric impl to new RT impl

[FoghostCn]

migrate old RT metric impl to new RT impl , related to #2376

1. simplify rt usage
2. fix: metric tag application -> application_name
3. fix: dubbo_registry_notify_num_last to metric type gauge

[sonarcloud]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
0 Code Smells

No Coverage information
No Duplication information

[codecov-commenter]

Codecov Report

Merging #2390 (585593a) into main (c9c5a46) will increase coverage by 0.02%.
The diff coverage is 0.00%.

❗ Current head 585593a differs from pull request most recent head a24153b. Consider uploading reports for the commit a24153b to get more accurate results

@@            Coverage Diff             @@
##             main    #2390      +/-   ##
==========================================
+ Coverage   45.05%   45.08%   +0.02%     
==========================================
  Files         306      306              
  Lines       18692    18652      -40     
==========================================
- Hits         8422     8409      -13     
+ Misses       9393     9368      -25     
+ Partials      877      875       -2     

Files Changed	Coverage Δ
metrics/api.go	0.00% <0.00%> (ø)
metrics/common.go	0.00% <0.00%> (ø)

... and 1 file with indirect coverage changes

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[ev1lQuark]

LGTM

[chickenlj]

LGTM.