Fixes actions#454

Add support for passing a list of docker images to attest.

* **action.yml**
  - Add a new input parameter `subject-images` to accept a list of docker images.
  - Update the `runs` section to handle the `subject-images` input.

* **src/main.ts**
  - Import `parseMultiImageInput` function from `utils.ts`.
  - Add logic to handle the `subject-images` input and process multiple docker images for attestation.

* **README.md**
  - Update the documentation to include usage instructions for the `subject-images` input.
  - Add an example for attesting multiple docker images.

* **__tests__/main.test.ts**
  - Add test cases to verify the functionality of attesting multiple docker images using the `subject-images` input.

* **src/utils.ts**
  - Add a new file to include the `parseMultiImageInput` function to parse the `subject-images` input.

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For more details, open the [Copilot Workspace session](https://copilot-workspace.githubnext.com/actions/attest-build-provenance/issues/454?shareId=XXXX-XXXX-XXXX-XXXX).

Update `.github/linters/.markdown-lint.yml` to configure markdown linting rules.

* **Ordered list item prefix**
  - Set style to 'one' for MD029

* **Line length**
  - Set line length to 80 for MD013
  - Disable line length check for code blocks, tables, headings, headings with children, and code lines

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For more details, open the [Copilot Workspace session](https://copilot-workspace.githubnext.com/GIgako19929/attest-build-provenance?shareId=XXXX-XXXX-XXXX-XXXX).

Add logic to process each image for attestation and handle errors in `src/main.ts`.

* **src/main.ts**
  - Add logic to process each image for attestation.
  - Add logic to handle errors and fail the workflow run if an error is encountered.
  - Add `processImageForAttestation` function to process images.

* **__tests__/main.test.ts**
  - Add test cases to verify the processing of each image for attestation.
  - Add test cases to verify the handling of errors and failing the workflow run.

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For more details, open the [Copilot Workspace session](https://copilot-workspace.githubnext.com/GIgako19929/attest-build-provenance?shareId=XXXX-XXXX-XXXX-XXXX).

Update main function to process images and handle errors

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