Use build-local dir instead of project deps in samples

[adinauer]

Our Spring Boot + OTel samples currently use project dependencies (e.g. project(":sentry-opentelemetry:sentry-opentelemetry-bom")), which:

• Pollutes the buildscript classpath, undermining test isolation
• Makes the samples uncopyable by customers (who won't have project references)
• Masks real compatibility issues (e.g. OTel + Spring Boot version conflicts hidden by the BOM being pulled via project ref rather than a real artifact)

Proposed change

Publish SDK artifacts to a build-local Maven directory during CI and configure the samples to resolve from that directory. This preserves per-PR test coverage without the classpath isolation problems of mavenLocal (which has shared global state) and without requiring publishing to Maven Central.

Scope

• Set up a build-local publish step that outputs to a local directory (e.g. build/local-repo)
• Update sample build.gradle.kts files to add that local dir as a repository
• Use published coordinates (e.g. io.sentry:sentry-opentelemetry-bom) instead of project references in dependencyManagement
• Keep samples using released/stable version strings so customers can copy them as-is

Out of scope

• Moving samples to Maven Central publishing
• Fully separating samples from test infrastructure (tracked separately)

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View Junior Session in Sentry

[linear-code]

JAVA-625

[adinauer]

Ideally we change this for all our samples but as a first step we can take care of the OTel samples.