fix(adasvc): do not load adaptive service filter if not set

[justxuewei]

What this PR does:

Which issue(s) this PR fixes:
Fixes #

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[codecov-commenter]

Codecov Report

Merging #1735 (b4d8431) into 3.0 (bf7c407) will decrease coverage by 0.14%.
The diff coverage is 10.00%.

@@            Coverage Diff             @@
##              3.0    #1735      +/-   ##
==========================================
- Coverage   42.84%   42.70%   -0.15%     
==========================================
  Files         256      256              
  Lines       14774    14782       +8     
==========================================
- Hits         6330     6312      -18     
- Misses       7722     7748      +26     
  Partials      722      722              

Impacted Files	Coverage Δ
config/service_config.go	10.60% <0.00%> (-0.16%)	⬇️
config/provider_config.go	19.04% <25.00%> (+0.23%)	⬆️
filter/metrics/filter.go	85.00% <0.00%> (-15.00%)	⬇️
metadata/report/delegate/delegate_report.go	26.49% <0.00%> (-8.61%)	⬇️
protocol/dubbo3/dubbo3_invoker.go	55.65% <0.00%> (-1.74%)	⬇️
metrics/prometheus/reporter.go	26.85% <0.00%> (-1.72%)	⬇️
...tocol/rest/server/server_impl/go_restful_server.go	44.82% <0.00%> (+3.44%)	⬆️

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