fix: Resolve client version at runtime from pom.xml

[i-am-SR]

Description

Why is this change being made?

1. The library version was maintained in two places: pom.xml (2.2.0) and a hardcoded constant in VersionInfo (2.1.0). They had already drifted, so the SDK UserAgent header reported a stale version (AwsSecretCache/2.1.0), causing version misreporting in Secrets Manager service logs.
2. When adding its UserAgent suffix, the client overwrote any caller-provided USER_AGENT_SUFFIX on the SecretsManagerClientBuilder, discarding the upstream caller's UserAgent instead of preserving it.

What is changing?

1. pom.xml is now the single source of truth for the version. A Maven-filtered version.properties resource (version=${project.version}) is read at runtime by VersionInfo, with a safe unknown fallback that never throws.
2. The builder-based constructor now appends the caching identifier while preserving the caller's suffix: <caller-suffix> AwsSecretCache/<version>.
3. README.md install snippet no longer hardcodes a version, it points to Maven Central.

Related Links

• Issue #, if available: N/A

---

Testing

How was this tested?

1. unit testing withmvn clean test : BUILD SUCCESS, 46 tests, 0 failures;
2. New unit tests cover version resolution and all fallback paths

When testing locally, provide testing artifact(s):

1. Tests run: 46, Failures: 0, Errors: 0, Skipped: 0

---

Reviewee Checklist

Update the checklist after submitting the PR

• I have reviewed, tested and understand all changes
  If not, why:
• I have filled out the Description and Testing sections above
  If not, why:
• Build and Unit tests are passing
  If not, why:
• Unit test coverage check is passing
  If not, why:
• I have ensured no sensitive information is leaking (i.e., no logging of sensitive fields, or otherwise)
  If not, why:
• I have added explanatory comments for complex logic, new classes/methods and new tests
  If not, why:
• I have updated README/documentation (if needed)
  If not, why:
• I have clearly called out breaking changes (if any)
  If not, why:

---

Reviewer Checklist

All reviewers please ensure the following are true before reviewing:

• Reviewee checklist has been accurately filled out
• Code changes align with stated purpose in description
• Test coverage adequately validates the changes

---

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[codecov]

Codecov Report

❌ Patch coverage is 96.87500% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 94.42%. Comparing base (dc47d68) to head (d62d4c1).

Files with missing lines	Patch %	Lines
...etsmanager/caching/cache/internal/VersionInfo.java	95.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##                 v2     #200      +/-   ##
============================================
+ Coverage     91.83%   94.42%   +2.58%     
- Complexity       97      108      +11     
============================================
  Files             6        7       +1     
  Lines           245      269      +24     
  Branches         26       29       +3     
============================================
+ Hits            225      254      +29     
+ Misses           18       12       -6     
- Partials          2        3       +1     

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

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.