[Enhancement] (FE) Convert intra FE-to-FE calls to HTTPS when enabled

[nsivarajan]

What problem does this PR solve?

Issue Number: close #xxx

Related PR: #xxx

Problem Summary:

Currently, Doris provides an enable_https switch to enforce HTTPS connections. In hardened deployments, HTTP is completely disabled by setting http_port = 0. However, intra FE-to-FE communication still relies on HTTP, causing failures in edit log and checkpoint synchronisation when HTTPS is enabled.

This PR enhances HTTPS support by automatically converting intra FE-to-FE communication to HTTPS when enable_https=true, without introducing any new configuration, leveraging mysql_ssl_default_ca_certificate created for https connection. When enable_https=false, behavior remains unchanged. This ensures secure and seamless FE-to-FE communication without breaking existing workflows.

Release note

None

Check List (For Author)

• Test

  • Regression test
  • Unit Test
  • Manual test (add detailed scripts or steps below)
  • No need to test or manual test. Explain why:
    • This is a refactor/code format and no logic has been changed.
    • Previous test can cover this change.
    • No code files have been changed.
    • Other reason

• Behavior changed:

  • No.
  • Yes.

• Does this need documentation?

  • No.
  • Yes.

Check List (For Reviewer who merge this PR)

• Confirm the release note
• Confirm test cases
• Confirm document
• Add branch pick label

[hello-stephen]

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1. What problem was fixed (it's best to include specific error reporting information). How it was fixed.
2. Which behaviors were modified. What was the previous behavior, what is it now, why was it modified, and what possible impacts might there be.
3. What features were added. Why was this function added?
4. Which code was refactored and why was this part of the code refactored?
5. Which functions were optimized and what is the difference before and after the optimization?