tiproxy: support multiple external pd clusters

[YangKeao]

After pingcap/tiproxy#1126, TiProxy supports multiple external pd clusters. Here I modified the tidb-operator to support to define the external pd clusters for a tiproxy deployment:

1. Allow to deploy TiProxy without PD.
2. Support to listen to a range of port.

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[codecov-commenter]

Codecov Report

❌ Patch coverage is 60.00000% with 8 lines in your changes missing coverage. Please review.
✅ Project coverage is 37.50%. Comparing base (f1c9aea) to head (0f0e9c3).
⚠️ Report is 13 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6831      +/-   ##
==========================================
+ Coverage   37.16%   37.50%   +0.33%     
==========================================
  Files         390      392       +2     
  Lines       22360    22446      +86     
==========================================
+ Hits         8310     8418     +108     
+ Misses      14050    14028      -22     

Flag	Coverage Δ
unittest	37.50% <60.00%> (+0.33%)	⬆️

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[YangKeao]

/retest

[ti-chi-bot]

@YangKeao: The following test failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
pull-e2e	0f0e9c3	link	true	/test pull-e2e

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