branch-4.1: [fix](cloud) Prevent old clients from decoding unknown MetaServiceCode as OK (#64148)

[wyxxxcat]

pick: #64148
Problem Summary: Older BE versions may treat unknown meta service enum codes as OK under proto2 semantics. Add a request capability marker so MS only returns MS_TOO_BUSY to BE versions that can handle it, and downgrade otherwise.

[hello-stephen]

Thank you for your contribution to Apache Doris.
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Please clearly describe your PR:

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?

[wyxxxcat]

run buildall

[wyxxxcat]

run buildall

[hello-stephen]

Cloud UT Coverage Report

Increment line coverage 62.96% (17/27) 🎉

Increment coverage report
Complete coverage report

Category	Coverage
Function Coverage	77.62% (1904/2453)
Line Coverage	64.46% (34013/52769)
Region Coverage	64.49% (17214/26693)
Branch Coverage	53.97% (9210/17064)

[hello-stephen]

FE UT Coverage Report

Increment line coverage 40.00% (12/30) 🎉
Increment coverage report
Complete coverage report

[hello-stephen]

BE UT Coverage Report

Increment line coverage 35.29% (6/17) 🎉

Increment coverage report
Complete coverage report

Category	Coverage
Function Coverage	58.01% (24293/41879)
Line Coverage	42.10% (242360/575665)
Region Coverage	38.18% (191394/501274)
Branch Coverage	39.47% (87043/220529)

[hello-stephen]

BE Regression && UT Coverage Report

Increment line coverage 100.00% (17/17) 🎉

Increment coverage report
Complete coverage report

Category	Coverage
Function Coverage	73.40% (30024/40906)
Line Coverage	57.32% (328187/572542)
Region Coverage	54.16% (273090/504189)
Branch Coverage	55.16% (121709/220660)

[hello-stephen]

FE Regression Coverage Report

Increment line coverage 56.67% (17/30) 🎉
Increment coverage report
Complete coverage report