pd-ctl: use url to construct the request path of list keyspace

[YuJuncen]

What problem does this PR solve?

Issue Number: Close #9385

What is changed and how does it work?

Use url to construct the requesting url.

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)

> bin/pd-ctl keyspace list --page_token=9 -u '127.0.0.1:35657'
{
    "keyspaces": [
        {
            "id": 9,
            "name": "ks-8531587855240960849",
            "state": "ENABLED",
            "created_at": 1749191139,
            "state_changed_at": 1749191139
        },
        {
            "id": 10,
            "name": "ks-13162349455034470458",
            "state": "ENABLED",
            "created_at": 1749191139,
            "state_changed_at": 1749191139
        }
    ],
    "next_page_token": ""
}

• No code

Code changes

• Has the configuration change
• Has HTTP API interfaces changed (Don't forget to add the declarative for the new API)
• Has persistent data change

Side effects

• Possible performance regression
• Increased code complexity
• Breaking backward compatibility

Related changes

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

Release note

Fixed a bug that caused `pd-ctl keyspace list` returns 404 when only specifing `--page_token`.

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: bufferflies, okJiang

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• OWNERS [bufferflies]

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2025-06-06 07:56:24.968854753 +0000 UTC m=+601271.171200011: ☑️ agreed by okJiang.
• 2025-06-09 09:31:24.747270553 +0000 UTC m=+261062.975585829: ☑️ agreed by bufferflies.

[YuJuncen]

/run-check-issue-triage-complete

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 76.09%. Comparing base (29ead01) to head (94e8943).
Report is 2 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #9386      +/-   ##
==========================================
- Coverage   76.10%   76.09%   -0.01%     
==========================================
  Files         478      478              
  Lines       74707    74698       -9     
==========================================
- Hits        56853    56845       -8     
  Misses      14316    14316              
+ Partials     3538     3537       -1     

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