feat: add source for single file

[deepu9]

Closes #18

1. Added ability to download a file from an url.
2. Also, run the checksum validation on the file and
3. Finally move the downloaded file to a source folder.

[mirkobrombin]

LGTM

[kbdharun]

LGTM, thanks for your contribution.

Tested the changes locally and made a few improvements:

1. Improved Error handling for checksum in the source types.
2. Updated docs to reflect the changes.
3. Updated Gitignore file to not commit Vib generated/config files to the repository.
4. Update website's index example (unrelated to PR).

Recipe used for testing:

name: Testing recipe
id: test
stages:
  - id: build
    base: ghcr.io/vanilla-os/pico:main
    singlelayer: false
    labels:
      maintainer: Vanilla OS Contributors
    modules:
      - name: build-app
        type: shell
        source:
          type: file
          url: https://github.com/Vanilla-OS/Vib/releases/download/v0.7.3/vib
          checksum: 5c4dbe2bef7c23175ad1c8230840a6b3c91c3ab3ed1eb026d9bc4b6eb382333d
        commands:
          - ./vib -v 

[deepu9]

LGTM, thanks for your contribution.

Tested the changes locally and made a few improvements:

1. Improved Error handling for checksum in the source types.
2. Updated docs to reflect the changes.
3. Updated Gitignore file to not commit Vib generated/config files to the repository.
4. Update website's index example (unrelated to PR).

Recipe used for testing:

name: Testing recipe
id: test
stages:
  - id: build
    base: ghcr.io/vanilla-os/pico:main
    singlelayer: false
    labels:
      maintainer: Vanilla OS Contributors
    modules:
      - name: build-app
        type: shell
        source:
          type: file
          url: https://github.com/Vanilla-OS/Vib/releases/download/v0.7.3/vib
          checksum: 5c4dbe2bef7c23175ad1c8230840a6b3c91c3ab3ed1eb026d9bc4b6eb382333d
        commands:
          - ./vib -v 

Thanks @kbdharun. My apologies for not updating the docs.