Setup RDF and schema URL redirections for 3.1

[bact]

These URL redirections are needed for 3.1 to work:

• https://spdx.org/schema/3.1/spdx-json-schema.json
• https://spdx.org/rdf/3.1/spdx-model.ttl
• https://spdx.org/rdf/3.1/spdx-context.jsonld

[bact]

During development period, the redirection setup could look like:

• https://spdx.org/schema/3.1/spdx-json-schema.json -> https://spdx.github.io/spdx-spec/v3.1-dev/rdf/spdx-model.jsonld
• https://spdx.org/rdf/3.1/spdx-model.ttl -> https://spdx.github.io/spdx-spec/v3.1-dev/rdf/spdx-model.ttl
• https://spdx.org/rdf/3.1/spdx-context.jsonld -> https://spdx.github.io/spdx-spec/v3.1/rdf/spdx-context.jsonld