[MINOR] fix: Change to get coordinator appCurrent value from metrics

[maobaolong]

What changes were proposed in this pull request?

Change to get coordinator appCurrent value from metrics

Why are the changes needed?

Keep consistent with appTotality, and in case of incorrect result returned from getAppIds.

Does this PR introduce any user-facing change?

No.

How was this patch tested?

No need.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 1 line in your changes missing coverage. Please review.

Project coverage is 52.40%. Comparing base (d170004) to head (946633a).
Report is 9 commits behind head on master.

Files with missing lines	Patch %	Lines
.../coordinator/web/resource/ApplicationResource.java	0.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #2129      +/-   ##
============================================
+ Coverage     51.72%   52.40%   +0.68%     
+ Complexity     3275     3117     -158     
============================================
  Files           524      489      -35     
  Lines         29833    25756    -4077     
  Branches       2556     2420     -136     
============================================
- Hits          15431    13498    -1933     
+ Misses        13400    11369    -2031     
+ Partials       1002      889     -113     

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[github-actions]

Test Results

 2 851 files   - 31   2 851 suites   - 31   5h 47m 1s ⏱️ - 10m 2s
 1 019 tests ± 0   1 017 ✅  -  1   1 💤 ±0  1 ❌ +1 
12 808 runs   - 60  12 792 ✅  - 61  15 💤 ±0  1 ❌ +1 

For more details on these failures, see this check.

Results for commit 946633a. ± Comparison against base commit 1d61e67.

[maobaolong]

The failed test is not caused by this PR, it seems a flaky test.

Error:  Tests run: 14, Failures: 1, Errors: 0, Skipped: 0, Time elapsed: 228.076 s <<< FAILURE! - in org.apache.uniffle.test.QuorumTest
Error:  case8  Time elapsed: 184.125 s  <<< FAILURE!
org.opentest4j.AssertionFailedError: expected: <true> but was: <false>
	at org.junit.jupiter.api.AssertionUtils.fail(AssertionUtils.java:55)
	at org.junit.jupiter.api.AssertTrue.assertTrue(AssertTrue.java:40)
	at org.junit.jupiter.api.AssertTrue.assertTrue(AssertTrue.java:35)
	at org.junit.jupiter.api.Assertions.assertTrue(Assertions.java:179)
	at org.apache.uniffle.test.QuorumTest.case8(QuorumTest.java:829)

[jerqi]

LGTM.

[maobaolong]

@jerqi Thanks for your review!