fix: fix xline member add bug

[Phoenix500526]

Please briefly answer these questions:

• what problem are you trying to solve? (or if there's no problem, what's the motivation for this change?)

1. close issue [Bug]: Failed to add a new member node4 to a three-nodes xline cluster #661

• what changes does this pull request make?

1. enrich the cluster_validation test case to cover the whole member add process.
2. sort the self_peer_urls to match the member.peer_urls and add client URLs
3. add a single node cluster mode flag to specify a special case —— scale out from one node cluster to a two nodes clsuter.

• are there any non-obvious implications of these changes? (does it break compatibility with previous versions, etc)

[codecov]

Codecov Report

Attention: Patch coverage is 91.66667% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 75.60%. Comparing base (e35b35a) to head (2c9504c).
Report is 92 commits behind head on master.

Files	Patch %	Lines
crates/curp/src/members.rs	91.66%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #658      +/-   ##
==========================================
+ Coverage   75.55%   75.60%   +0.04%     
==========================================
  Files         180      186       +6     
  Lines       26938    27488     +550     
  Branches    26938    27488     +550     
==========================================
+ Hits        20353    20782     +429     
- Misses       5366     5431      +65     
- Partials     1219     1275      +56     

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[mergify]

@Phoenix500526 Your PR is in conflict and cannot be merged.

[mergify]

@Phoenix500526 Convert your pr to draft since CI failed

[mergify]

@Phoenix500526 Convert your pr to draft since CI failed

[mergify]

@Phoenix500526 Your PR is in conflict and cannot be merged.

[mergify]

@Phoenix500526 Your PR is in conflict and cannot be merged.