feat: add egctl experimental dashboard envoy-proxy to render the admin dashboard for the proxy

[hanxiaop]

What type of PR is this?

/feature

What this PR does / why we need it:

Render the admin dashboard for the proxy, to see things like configdumps without extra steps.

[hanxiaop]

Sample cmd out:

 ./egctl x dashboard envoy-proxy -n envoy-gateway-system envoy-engw-eg-a9c23fbb-558f94486c-82wh4
http://localhost:19000

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 110 lines in your changes are missing coverage. Please review.

Project coverage is 63.00%. Comparing base (4c79ef9) to head (8bc249f).
Report is 7 commits behind head on main.

Files	Patch %	Lines
internal/cmd/egctl/envoy_dashboard.go	0.00%	98 Missing ⚠️
internal/cmd/egctl/dashboard.go	0.00%	11 Missing ⚠️
internal/cmd/egctl/experimental.go	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2669      +/-   ##
==========================================
- Coverage   63.38%   63.00%   -0.39%     
==========================================
  Files         119      121       +2     
  Lines       19098    19574     +476     
==========================================
+ Hits        12106    12332     +226     
- Misses       6193     6441     +248     
- Partials      799      801       +2     

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[hanxiaop]

@shawnh2 Thank you for the review! I think I have addressed all the comments.

[shawnh2]

LGTM, thanks