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. Generate the correct TiProxy config according to the newly added Spec.
2. Support to listen to a range of port.

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[codecov-commenter]

Codecov Report

❌ Patch coverage is 80.70175% with 11 lines in your changes missing coverage. Please review.
✅ Project coverage is 37.31%. Comparing base (f1c9aea) to head (1985513).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6831      +/-   ##
==========================================
+ Coverage   37.16%   37.31%   +0.14%     
==========================================
  Files         390      390              
  Lines       22360    22410      +50     
==========================================
+ Hits         8310     8362      +52     
+ Misses      14050    14048       -2     

Flag	Coverage Δ
unittest	37.31% <80.70%> (+0.14%)	⬆️

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