Missing absolute path validation for several fields

[nayuta723]

runc does not validate absolute path requirements for several fields as mandated by the OCI Runtime Specification.

The relevant fields are listed below.

• hooks.*.path
  • https://github.com/opencontainers/runtime-spec/blob/main/config.md#posix-platform-hooks
• linux.namespaces[].path
  • https://github.com/opencontainers/runtime-spec/blob/main/config-linux.md#namespaces
• linux.maskedPaths
  • https://github.com/opencontainers/runtime-spec/blob/main/config-linux.md#masked-paths
• linux.readonlyPaths
  • https://github.com/opencontainers/runtime-spec/blob/main/config-linux.md#readonly-paths

If there is some reason runc intentionally does not support this, I would know it, and if just a miss, I would improve.