[WIP] feat: build docker image optimisation for reusing the jar again

[shubham19may]

Description

Fixes # (issue)

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

How Has This Been Tested?

Will be testing soon

Screenshots or Recordings

Documentation

• Documentation Link: [link to README, olake.io/docs, or olake-docs]
• N/A (bug fix, refactor, or test changes only)

Related PR's (If Any):

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Note

Restructures Docker build to separate a runtime base and reuse a prebuilt JAR/specs, and updates release tooling to produce reproducible Maven JARs and reuse them when sources are unchanged.

• Docker image:
  • Create runtime-base from alpine:3.18 with OpenJDK 17 and embed prebuilt olake-iceberg-java-writer.jar plus destination specs.
  • Add separate Go builder stage; final stage FROM runtime-base copies built olake binary and driver spec.
• Release tooling (release-tool.sh):
  • Make Maven builds reproducible using SOURCE_DATE_EPOCH and -Dproject.build.outputTimestamp.
  • Record module commit in target/.built-commit and add ensure_java_jar to reuse the prebuilt JAR when sources haven't changed; replace direct build_java_project with ensure_java_jar.

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