build: use global action step

[sebastian-alfers]

Summary

• Add akka/github-actions-scripts/setup_global_resolver@main step to all CI workflow files (after JDK/GraalVM setup in each job)
• Remove the https://repo.akka.io/maven/github_actions resolver from all SBT build files (build.sbt, project/plugins.sbt, and all sample projects) and Maven pom.xml files
• Add ## Build Token section to README.md with instructions for local development

Test plan

• Verify all CI workflows pass with the new global resolver step
• Verify that local builds work using the token instructions in README

🤖 Generated with Claude Code

[johanandren]

Resolver not picked up for maven plugins it seems

[sebastian-alfers]

Hemm, the error is:

Error:  Failed to execute goal com.lightbend.akka.grpc:akka-grpc-maven-plugin:2.5.10:generate (default) on project shopping-cart-service: Execution default of goal com.lightbend.akka.grpc:akka-grpc-maven-plugin:2.5.10:generate failed: error occurred while compiling protobuf files: Unsupported platform: protoc-3.25.8-linux-x86_64.exe -> [Help 1]

Is that a missing resolver symptom?