feat: add support for footnotes in markdown parsing

[akoso]

This commit introduces the ability to parse footnotes in markdown content. It includes updates to the parsing logic to handle footnote references and definitions, as well as corresponding tests to ensure functionality. Additionally, the package dependencies have been updated to include remark-footnotes for enhanced markdown processing.

Example

Input:

"Some random text with a reference[^1].  \nAnd with another[^2] one.\n\n[^1]: https://github.com/tryfabric/martian/pull/74\n[^2]: https://www.google.com/"

Output:

[
  {
    object: "block",
    type: "paragraph",
    paragraph: {
      rich_text: [
        {
          type: "text",
          annotations: {
            bold: false,
            strikethrough: false,
            underline: false,
            italic: false,
            code: false,
            color: "default",
          },
          text: {
            content: "Some random text with a reference",
            link: undefined,
          },
        },
        {
          type: "text",
          annotations: {
            bold: false,
            strikethrough: false,
            underline: false,
            italic: false,
            code: false,
            color: "default",
          },
          text: {
            content: "[1]",
            link: undefined,
          },
        },
        {
          type: "text",
          annotations: {
            bold: false,
            strikethrough: false,
            underline: false,
            italic: false,
            code: false,
            color: "default",
          },
          text: {
            content: ".",
            link: undefined,
          },
        },
      ],
    },
  },
  {
    object: "block",
    type: "paragraph",
    paragraph: {
      rich_text: [
        {
          type: "text",
          annotations: {
            bold: false,
            strikethrough: false,
            underline: false,
            italic: false,
            code: false,
            color: "default",
          },
          text: {
            content: "And with another",
            link: undefined,
          },
        },
        {
          type: "text",
          annotations: {
            bold: false,
            strikethrough: false,
            underline: false,
            italic: false,
            code: false,
            color: "default",
          },
          text: {
            content: "[2]",
            link: undefined,
          },
        },
        {
          type: "text",
          annotations: {
            bold: false,
            strikethrough: false,
            underline: false,
            italic: false,
            code: false,
            color: "default",
          },
          text: {
            content: " one.",
            link: undefined,
          },
        },
      ],
    },
  },
  {
    object: "block",
    type: "paragraph",
    paragraph: {
      rich_text: [
        {
          type: "text",
          annotations: {
            bold: false,
            strikethrough: false,
            underline: false,
            italic: false,
            code: false,
            color: "default",
          },
          text: {
            content: "1. ",
            link: undefined,
          },
        },
        {
          type: "text",
          annotations: {
            bold: false,
            strikethrough: false,
            underline: false,
            italic: false,
            code: false,
            color: "default",
          },
          text: {
            content: "https://github.com/tryfabric/martian/pull/74",
            link: {
              type: "url",
              url: "https://github.com/tryfabric/martian/pull/74",
            },
          },
        },
      ],
    },
  },
  {
    object: "block",
    type: "paragraph",
    paragraph: {
      rich_text: [
        {
          type: "text",
          annotations: {
            bold: false,
            strikethrough: false,
            underline: false,
            italic: false,
            code: false,
            color: "default",
          },
          text: {
            content: "2. ",
            link: undefined,
          },
        },
        {
          type: "text",
          annotations: {
            bold: false,
            strikethrough: false,
            underline: false,
            italic: false,
            code: false,
            color: "default",
          },
          text: {
            content: "https://www.google.com/",
            link: {
              type: "url",
              url: "https://www.google.com/",
            },
          },
        },
      ],
    },
  },
]

And in Notion: