Update licensing information

Dependencies

• [2] OAOH3QOZ Extract metadata into separate crate
• [*] R524JUUE Implement metadata & price directives
• [*] SEEWF7KX Implement metadata on transactions

Change contents

• edit in beancount/metadata/src/link.rs at line 1
  [4.1873]

  [4.1874]
  + // SPDX-FileCopyrightText: 2023 - 2024 Markus Haug (Korrat)

  + //

  + // SPDX-License-Identifier: EUPL-1.2

  +
• edit in beancount/metadata/src/lib.rs at line 1
  [5.2624]

  [2.451]
  + // SPDX-FileCopyrightText: 2023 - 2024 Markus Haug (Korrat)

  + //

  + // SPDX-License-Identifier: EUPL-1.2

  +
• edit in beancount/metadata/src/kv.rs at line 1
  [4.4555]

  [4.4556]
  + // SPDX-FileCopyrightText: 2023 - 2024 Markus Haug (Korrat)

  + //

  + // SPDX-License-Identifier: EUPL-1.2

  +
• edit in beancount/metadata/src/kv/common_keys.rs at line 1
  [4.9050]

  [4.9051]
  + // SPDX-FileCopyrightText: 2023 - 2024 Markus Haug (Korrat)

  + //

  + // SPDX-License-Identifier: EUPL-1.2

  +
• edit in beancount/metadata/Cargo.toml at line 1
  [2.812]

  [2.813]
  + # SPDX-FileCopyrightText: 2023 - 2024 Markus Haug (Korrat)

  + #

  + # SPDX-License-Identifier: EUPL-1.2

  +