Fix host UID/GID leakage in copyFileToContainer TAR entries

[ym0506]

Fixes #11487

Problem

When copyFileToContainer copies a MountableFile, TAR entries are created from host files. The TAR metadata may carry host UID/GID values into the container.

On rootless Docker setups, those IDs may be unmapped, causing permission/ownership issues (e.g. Keycloak dev service failing to read copied config).

Solution

Normalize TAR entry ownership for MountableFile copies:

• set TAR entry uid=0
• set TAR entry gid=0

This avoids leaking host identity into the container filesystem metadata.

Tests

Added MountableFileTest#tarEntriesShouldUseRootOwnership to verify generated TAR entries use UID/GID 0.

Related

• testcontainers-java issue [Bug]: #11487
• Keycloak Dev Service fails to start on rootless Docker setup quarkusio/quarkus#45940