Add Layer info data as a layer attribute

[hanbyul-here]

Part of #823

Heavily edited after the last time I opened this PR

With this pr, layer can include info attribute. info consists of

info:
  modal: 
    subtitle: |
      ::markdown subtitle in markdown
    contents: |
      ::markdown contents in markdown
  template:
        source: string
        spatialExtent: string
        latency: string
        unit: string

I added a sandbox page to trigger the modal. https://deploy-preview-843--veda-ui.netlify.app/sandbox/sandboxLayerInfo

@faustoperez Currently, there is no easy way to determine if the link the user uses is an external or an internal link. (The link is just part of the HTML that a user passes as a part of Layerdata.) So I think we might have to skip the external link icons. :[

I am not implementing the link on top of the header, since I can pick that component up from the other branch currently working on (#829)

Details of technical implementation: This PR required an Implementation of processing markdown in frontmatter in stringfy-yml-func.

• I thought about passing Markdown as it is and delegating the rendering of it to the front-end, but it will increase the load of front-end work at this point. (Integrating it with our current MDX system for rendering stories and datasets seems challenging.)
• Initially considered using our system's markdown parsers (remark and rehype), but they are pure ES modules requiring rewiring in the pipeline, which I wanted to avoid in this PR. Therefore, I chose a different markdown parser.
• It's important to note that info.modal.subtitle and info.modal.contents should only contain markdown, not MDX, to exclude custom components.

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[j08lue]

We need nice property titles, not just slug-like keys, please.

[hanbyul-here]

I think I poorly communicated what the code does in this PR. I will close this for now and open it again after making it clear.

[j08lue]

Looks good and the choice of making it all Markdown is solid for now (see comment below).

[j08lue]

All Markdown seems like a good solution for now.

At some point in the future, we will want this to be more structured (and probably coming from STAC), following the example of Planetary Computer. But free form is fine for now.

[hanbyul-here]

Yeah, I agree. Especially since our current application also asks for structured data (why info has a separate section for template). We would need more streamlined thoughts about how to handle this layer information before though. I can't think of a straightforward way of having both descriptive layerinfo and structured layerinfo without manual edits and duplication of the data.

[sandrahoang686]

🔧 : Mispelled from and should no2 be hardcoded here?

[hanbyul-here]

I moved markdown level data to the dataset (infoDescription - please let me know if there is a better way to name these.), left info to layer level. Added these two to documentation ticket: #842