Description:
Add an optional multiline cache-path input that overrides the main dependency cache paths for the package manager selected by cache.

- uses: actions/setup-java@v5
  with:
    distribution: temurin
    java-version: '21'
    cache: maven
    cache-path: |
      /custom/maven/repository

When omitted, the existing Maven, Gradle, and sbt defaults remain unchanged.

Proposed behavior:

• cache-path accepts one or more newline-separated paths.
• Supplied paths replace the selected package manager's main dependency paths.
• The action does not configure the build tool; users must ensure it uses the same paths.
• Maven and Gradle wrapper caches remain independently managed.
• Restore and post-job save use identical resolved paths.
• Existing behavior and cache keys remain unchanged when the input is omitted.
• Paths and exclusion patterns supported by actions/cache remain supported.

Examples:

# Gradle
with:
  cache: gradle
  cache-path: /custom/gradle-home/caches
env:
  GRADLE_USER_HOME: /custom/gradle-home

# sbt
with:
  cache: sbt
  cache-path: |
    /custom/ivy/cache
    /custom/coursier/cache

Direct actions/cache usage should remain the documented option for advanced keying, fallback keys, and unusual cache topology.

Related: #680

Justification:
Maven, Gradle, and sbt all allow users to relocate their dependency caches. The built-in caching currently uses hardcoded locations, requiring affected users to disable it and reproduce setup-java's cache behavior with actions/cache.

Although cache-primary-key can be reused, it is only computed when built-in caching is enabled, which also performs an unnecessary restore against the default paths. A cache-path override preserves setup-java's simple caching experience for a standard build-tool configuration while keeping existing behavior fully backward compatible.

Acceptance criteria:

• Supports Maven, Gradle, and sbt.
• Supports multiline paths and exclusion patterns accepted by actions/cache.
• Preserves existing defaults when omitted.
• Uses custom paths for both restore and save.
• Includes unit and end-to-end coverage.
• Documents when direct actions/cache usage is preferable.

Are you willing to submit a PR?
Yes.