Migrate to Maven Central Portal from OSSRH for RIC & Core Packages. RIC Version Bump to 2.8.4

[M-Elsaeed]

Issue #, if available:

Description of changes: Migrate to Maven Central Portal Publishing instead of OSSRH for aws-lambda-java-core and aws-lambda-java-runtime-interface-client

For Other Packages, they we will be following the same approach in aws-lambda-java-core. Only aws-lambda-java-runtime-interface-client is different since, per deployment, it has an uber-jar and platform-specific jars.

Target (OCI, Managed Runtime, both): Both

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

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 64.74%. Comparing base (434185b) to head (45a4e42).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##               main     #565   +/-   ##
=========================================
  Coverage     64.74%   64.74%           
  Complexity      194      194           
=========================================
  Files            33       33           
  Lines           939      939           
  Branches        132      132           
=========================================
  Hits            608      608           
  Misses          282      282           
  Partials         49       49           

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