Add support for funding metadata key

[aleixalcacer]

I have added basic support for funding as indicated at https://assets.ctfassets.net/o78em1y1w4i4/3ro3yQff1q67JHmLi1sAqV/1348e3852f277867230fc4b84a801734/elsdoc-1.pdf.

It can be used in the following way:

---
...
funding:
     statement: This work is supported by AAA [aaa name]
...
---

However, I haven't found any elegant option to support:

---
...
funding: This work is supported by AAA [aaa name]
...
---

My suspicion is that the funding keyword is not well parsed in quarto, but I'm not sure.

Is it enough or should it be improved?

[dragonstyle]

Thanks for the PR. We should be normalizing that funding key and it appears we aren't doing it as expected in the pre-release. I'll have a look at that issue (I've created a linked to this) and then will merge this when I've confirmed it is working as expected!