xoffset works in .opts but not as kwarg.

I'm using `hvplot.labels`. The options for this seem quite finicky and under documented.

#### ALL software version info
hvplot '0.7.0'
holoviews '1.14.1'

#### Description of expected behavior and the observed behavior

This does not work:
```
df.hvplot.labels(x='Month', y='value', text='label', text_font_size='6pt', text_color='blue', xoffset=20)
```

This works:
```
df.hvplot.labels(x='Month', y='value', text='label', text_font_size='6pt', text_color='blue').opts(xoffset=20)
```

Also, in terms of changing the size and color of the labels, no amount of kwargs or opts seemed to work until I found this page and started passing the bokeh option names directly https://docs.bokeh.org/en/latest/docs/user_guide/styling.html#creating-custom-themes

Also, why does hvplot change the bokeh `x_offset` to `xoffset`? Wouldn't there be higher discoverability if the option names remained the same across the ecosystem? Maybe this is a silly question.

I guess my main point is that his page is under-documented: https://hvplot.holoviz.org/reference/pandas/labels.html