dashboard: support internal proxy (#2508)

[sre-bot]

cherry-pick #2508 to release-4.0

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Signed-off-by: Zheng Xiangsheng hundundm@gmail.com

What problem does this PR solve?

realize #532 Each pd can handle dashboard front-end resource requests

What is changed and how it works?

• config: add Dashboard.InternalProxy config
• dashboard: support internal proxy

Check List

Tests

• Unit test

Code changes

• Has configuration change

Related changes

• PR to update pingcap/docs/pingcap/docs-cn:
• Need to cherry-pick to the release branch

Release note

• The built-in dashboard supports internal proxy.

[HunDunDM]

/merge

[sre-bot]

Your auto merge job has been accepted, waiting for:

• 2509

[codecov-commenter]

Codecov Report

Merging #2511 into release-4.0 will increase coverage by 0.00%.
The diff coverage is 90.90%.

@@             Coverage Diff              @@
##           release-4.0    #2511   +/-   ##
============================================
  Coverage        76.99%   76.99%           
============================================
  Files              204      204           
  Lines            21864    21878   +14     
============================================
+ Hits             16834    16846   +12     
- Misses            3737     3747   +10     
+ Partials          1293     1285    -8     

Impacted Files	Coverage Δ
server/config/config.go	78.00% <ø> (ø)
pkg/dashboard/adapter/adapter.go	70.00% <84.61%> (ø)
pkg/dashboard/dashboard.go	90.69% <90.32%> (+2.46%)	⬆️
pkg/dashboard/adapter/redirector.go	94.23% <100.00%> (+0.61%)	⬆️
pkg/dashboard/uiserver/embedded_assets_rewriter.go	100.00% <100.00%> (ø)
tests/cluster.go	86.74% <100.00%> (ø)
server/schedulers/shuffle_hot_region.go	63.47% <0.00%> (-11.31%)	⬇️
server/region_syncer/client.go	81.67% <0.00%> (-4.59%)	⬇️
pkg/btree/btree.go	86.84% <0.00%> (-0.81%)	⬇️
... and 10 more

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[sre-bot]

/run-all-tests