feat: add spew dump for envoy-gateway config when starting up

[Xunzhuo]

What type of PR is this?

feat: add spew dump for envoy-gateway config when starting up, as the envoy gateway config grows bigger and more complex.

we should provide a direct way in log to see how the config recieved by eg looks like.

What this PR does / why we need it:

Which issue(s) this PR fixes:

[codecov]

Codecov Report

Merging #1425 (63e6e5c) into main (e518a0e) will increase coverage by 0.09%.
The diff coverage is 0.00%.

❗ Current head 63e6e5c differs from pull request most recent head 9973eb3. Consider uploading reports for the commit 9973eb3 to get more accurate results

@@            Coverage Diff             @@
##             main    #1425      +/-   ##
==========================================
+ Coverage   61.96%   62.05%   +0.09%     
==========================================
  Files          79       79              
  Lines       11271    11275       +4     
==========================================
+ Hits         6984     6997      +13     
+ Misses       3827     3821       -6     
+ Partials      460      457       -3     

Impacted Files	Coverage Δ
internal/cmd/server.go	15.75% <0.00%> (-0.45%)	⬇️

... and 2 files with indirect coverage changes

[qicz]

LGTM

[zirain]

could the output format be optimized, json or yaml is more readable.