Support reading labelled code cells

[jpfeuffer]

Hi!

Thanks for the neat plugin.
Unfortunately it does not support labels for referencing the outputs of qmd code blocks.
I started on at least ignoring the labels and saving them in the Block class.

Would be cool if we could generate an anchor for the admonition (or at least inside of it), to make it referencable with the default markdown reference syntax at least. Note this is not done yet.

My test:

---
title: "demo"
format:
  html:
    code-fold: true
jupyter: python3
---

For a demonstration of a line plot on a polar axis, see [here](#example-figure).
Test `{python} "hello " + str(4+5)`.

```{python}
#| echo: true
#| label: example-figure
#| tbl-cap: "dataframe" 
import pandas as pd

df = pd.DataFrame({
    "a": [1, 2, 3],
    "b": [100, 200, 300],
    "c": [0.01, 0.05, 0.001]
})
df
```

Sorry for the mix of topics and figure/tables 😄 was testing a lot of stuff. Can make it cleaner soon.

[jpfeuffer]

Now it also supports writing the label as id to the div.

I saw that for actual figures this is not necessary since quarto will add the label into the correct markdown figure.