Fix NPE in StaticTokenAuthProvider and UrlAuthProvider when required config property is absent

[Akanksha-kedia]

Summary

Both StaticTokenAuthProvider(AuthConfig) and UrlAuthProvider(AuthConfig) call .toString() directly on authConfig.getProperties().get(...) without a null check. When the required property (token or url) is absent from the config the result is an opaque NullPointerException with no indication of which property is missing.

This PR replaces the implicit null deref with an explicit check that throws IllegalArgumentException naming the missing property, giving operators an actionable error message.

// Before
String userToken = authConfig.getProperties().get(TOKEN).toString();  // NPE if TOKEN absent

// After
Object tokenValue = authConfig.getProperties().get(TOKEN);
if (tokenValue == null) {
    throw new IllegalArgumentException("Missing required auth config property: " + TOKEN);
}
String userToken = tokenValue.toString();

The same pattern is applied to UrlAuthProvider.

Test plan

• Existing auth provider unit tests pass
• Constructing either provider with a config missing the required property throws IllegalArgumentException with a clear message instead of NullPointerException

[Akanksha-kedia]

@xiangfu0 please review

[codecov-commenter]

Codecov Report

❌ Patch coverage is 0% with 10 lines in your changes missing coverage. Please review.
✅ Project coverage is 63.70%. Comparing base (1881884) to head (425509f).
⚠️ Report is 85 commits behind head on master.

Files with missing lines	Patch %	Lines
.../org/apache/pinot/common/auth/UrlAuthProvider.java	0.00%	6 Missing ⚠️
...che/pinot/common/auth/StaticTokenAuthProvider.java	0.00%	4 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master   #18456      +/-   ##
============================================
+ Coverage     63.40%   63.70%   +0.29%     
- Complexity     1679     1684       +5     
============================================
  Files          3253     3262       +9     
  Lines        198767   199832    +1065     
  Branches      30791    31033     +242     
============================================
+ Hits         126034   127297    +1263     
+ Misses        62659    62392     -267     
- Partials      10074    10143      +69     

Flag	Coverage Δ
custom-integration1	100.00% <ø> (ø)
integration	100.00% <ø> (ø)
integration1	100.00% <ø> (ø)
integration2	0.00% <ø> (?)
java-21	63.70% <0.00%> (+0.29%)	⬆️
temurin	63.70% <0.00%> (+0.29%)	⬆️
unittests	63.69% <0.00%> (+0.29%)	⬆️
unittests1	55.80% <0.00%> (+0.43%)	⬆️
unittests2	34.96% <0.00%> (+0.02%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[Akanksha-kedia]

@yashmayya please merge