feat: avoid log azure vault

[ndr-brt]

What this PR changes/adds

Avoid "severe" log on AzureVault when secret is not found.

Why it does that

To avoid misleading logs

Further notes

• test-covered the resolveSecret method
• remove useless CountDownLatch on AzureVaultExtensionTest

Linked Issue(s)

Closes #1962

Checklist

• added appropriate tests?
• performed checkstyle check locally?
• added/updated copyright headers?
• documented public classes/methods?
• added/updated relevant documentation?
• assigned appropriate label? (exclude from changelog with label no-changelog)
• formatted title correctly? (take a look at the CONTRIBUTING and styleguide for details)

[codecov-commenter]

Codecov Report

Merging #1963 (15e7226) into main (0e4b166) will increase coverage by 0.17%.
The diff coverage is 34.61%.

@@            Coverage Diff             @@
##             main    #1963      +/-   ##
==========================================
+ Coverage   62.80%   62.97%   +0.17%     
==========================================
  Files         782      782              
  Lines       16616    16643      +27     
  Branches     1080     1081       +1     
==========================================
+ Hits        10435    10481      +46     
+ Misses       5730     5712      -18     
+ Partials      451      450       -1     

Impacted Files	Coverage Δ
...spaceconnector/core/security/azure/AzureVault.java	26.56% <34.61%> (+26.56%)	⬆️
...smos/policy/store/CosmosPolicyDefinitionStore.java	91.30% <0.00%> (-6.32%)	⬇️
...osmos/policy/store/CosmosPolicyStoreExtension.java	0.00% <0.00%> (ø)
...store/schema/postgres/PolicyDefinitionMapping.java	100.00% <0.00%> (ø)
...sfer/core/transfer/TransferProcessManagerImpl.java	88.43% <0.00%> (+2.44%)	⬆️
.../policy/store/schema/SqlPolicyStoreStatements.java	92.30% <0.00%> (+7.69%)	⬆️

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