[rest] Propagate dependency read context in headers

[leaves12138]

Purpose

This replaces the broad grant-based approach from #8634 with a minimal,
backward-compatible mechanism for REST servers to receive the table that
initiated a runtime dependency read.

The dependency target is already identified by the existing table or data-token
endpoint path. This change adds an optional X-Paimon-Read-Via request header
containing the URL-encoded JSON Identifier of the outermost source table.

Changes

• Keep the existing Catalog, RESTCatalog, and RESTApi method signatures,
  endpoints, request/response DTOs, and OpenAPI specification unchanged.
• Derive a dependency-scoped CatalogContext only when a REST-backed table reads
  another table.
• Propagate that context through Blob View resolution and
  blob-descriptor.source-table.
• Preserve the outermost source table across nested dependency reads.
• Reuse the existing header.* support so both target getTable and data-token
  requests carry the context.

Old clients send no header, and old servers can ignore the optional header.

Security

X-Paimon-Read-Via is client-provided context, not authorization proof. The
server remains responsible for authenticating the caller and deciding whether
and how to use the source/target relationship.

Validation

• mvn -pl paimon-core -am -Pfast-build -DfailIfNoTests=false -DwildcardSuites=none -Dtest=CatalogEnvironmentTest,BlobDescriptorReaderFactoryTest,MockRESTCatalogTest test
  (132 tests passed)
• mvn -pl paimon-core -am -Pfast-build -DfailIfNoTests=false -DwildcardSuites=none '-Dtest=BlobTableTest#testBlobViewE2E+testForwardBlobViewReference' test
  (2 tests passed)
• mvn -pl paimon-core -am -DskipTests compile
• git diff --check