Get bwc version dynamically

[Hailong-am]

Description

remove hardcoded bwc version and replace it with fetching latest value from OpenSearch core

Related Issues

Resolves #[Issue number to be closed when this PR is merged]

Check List

• New functionality includes testing.
• New functionality has been documented.
• API changes companion pull request created.
• Commits are signed per the DCO using --signoff.
• Public documentation issue/PR created.

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[yuye-aws]

Rerunning the CI checks now

[Hailong-am]

checking on and trying suggestion in opensearch-project/opensearch-build#5178

/__e/node20/bin/node: /lib64/libm.so.6: version `GLIBC_2.27' not found (required by /__e/node20/bin/node)
/__e/node20/bin/node: /lib64/libc.so.6: version `GLIBC_2.28' not found (required by /__e/node20/bin/node)

[Hailong-am]

verified get version function in CI, it works as expected.

> Configure project :notifications
Extracted latest 2.x version: 2.19.0
=======================================
OpenSearch Build Hamster says Hello!
  Gradle Version        : 8.10.2
  OS Info               : Linux 6.5.0-10[25](https://github.com/opensearch-project/notifications/actions/runs/12113884869/job/33769553622?pr=987#step:6:26)-azure (amd64)
  JDK Version           : 21 (Eclipse Temurin JDK)
  JAVA_HOME             : /__t/Java_Temurin-Hotspot_jdk/21.0.5-11.0.LTS/x64
  Random Testing Seed   : F1A921C6D75F[27](https://github.com/opensearch-project/notifications/actions/runs/12113884869/job/33769553622?pr=987#step:6:28)CE
  In FIPS 140 mode      : false
=======================================