Migrating to modern maven publish plugin

[stigi]

Change description

We've been using a pretty old way of publishing to maven central and I'd like to migrate to a newer plugin:
https://github.com/vanniktech/gradle-maven-publish-plugin

The also mention that they are the spiritual successor to the approach we're currnetly using (aka Chris Banes initial implementation)

Benefits:

• Simpler setup. Less code to maintain
• Support for new Central Portal. This will make it easier to migrate our distrubution from the now legacy OSSHR system we're using right now. (migration docs)
• Full support for passing secrets via env vars

Test Plan

Tested locally, and build build signs and pulishes locally as expected:

$ ORG_GRADLE_PROJECT_signingInMemoryKey="...." \
  ORG_GRADLE_PROJECT_signingInMemoryKeyId="...." \
  ORG_GRADLE_PROJECT_signingInMemoryKeyPassword="..." \
  ./gradlew sdk:publishToMavenLocal

I compared the pom-default.xml files generated with the previous version and saw no difference.

Type of Change

• Bug fix
• Feature
• Enhancement

Guidelines

• A changeset is included, or the change is not noteworthy enough to warrant one