[AMORO-4211] Fix legacy Flink config loading

[NikhilUjjwal7]

Why are the changes needed?

Close #4211.

Legacy flink-conf.yaml can contain Flink metric filter values that start with *, for example:

xxx.metrics.filter.includes: *RSS:*:*;Heap:Used,Max:*

Close #xxx.

## Brief change log
Updated FlinkOptimizerContainer to load legacy flink-conf.yaml using Flink GlobalConfiguration.
Kept existing config.yaml loading behavior unchanged.
Added a unit-level regression test for legacy flink-conf.yaml containing metric filter values starting with *.

## How was this patch tested?

Added regression test :

TestFlinkOptimizerContainer#testReadLegacyFlinkConfigWithMetricFilterIncludes

Add screenshots for manual tests if appropriate
<img width="970" height="691" alt="Screenshot 2026-06-11 at 10 33 50 AM" src="https://github.com/user-attachments/assets/e5c7dad3-c761-41bc-9f2f-a69ca195ff8c" />



Run test locally before making a pull request
Ran locally :

./mvnw -pl amoro-ams -am \
  -Dtest=TestFlinkOptimizerContainer#testReadLegacyFlinkConfigWithMetricFilterIncludes \
  -Dsurefire.failIfNoSpecifiedTests=false \
  test
  
 Result : 
 Tests run: 1, Failures: 0, Errors: 0, Skipped: 0
BUILD SUCCESS
  
  
## Documentation


Does this pull request introduce a new feature? no
If yes, how is the feature documented? not applicable

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 30.06%. Comparing base (99fcc08) to head (dd27ec4).
⚠️ Report is 5 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #4249      +/-   ##
============================================
+ Coverage     23.09%   30.06%   +6.96%     
- Complexity     2706     4380    +1674     
============================================
  Files           463      680     +217     
  Lines         42826    55261   +12435     
  Branches       6044     7079    +1035     
============================================
+ Hits           9891    16614    +6723     
- Misses        32076    37395    +5319     
- Partials        859     1252     +393     

Flag	Coverage Δ
core	30.06% <100.00%> (?)
trino	?

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