Progress formatting options for `PercentageColumn`

Is your feature request related to a problem? Please describe.

I want to show a progress table using spectre. It works really well as it is, however, some operations take a really long time to complete, so I would like to be able to show more detailed progress values (e.g. 50.41% instead of just 50%).

The code responsible for this seems to be here:

https://github.com/spectreconsole/spectre.console/blob/813a53cdfaf24fb0ad759cc7af74d10b197c6618/src/Spectre.Console/Live/Progress/Columns/PercentageColumn.cs#L19-L24

And it doesn’t provide any outside entry points to customize this behavior.

Describe the solution you’d like

New ProgressColumn property of type string that serves as the format for task.Percentage.ToString(...). Potentially also a IFormattingProvider property too, but I personally need to use the current culture formatting anyway.

Describe alternatives you’ve considered

I could create my own ProgressColumn but I’d end up re-writing most of the stuff in the PercentageColumn.

Additional context

None that I could think of.

[patriksvensson]

@Tyrrrz Format strings are hard 😄, and I want to keep the number of support issues down if I can. We could however (in addition) add a new column where you get a lambda with the task, and where you return a string of your choice. Perhaps that would be a middle road?

[patriksvensson]

So, I’ve been thinking, and perhaps we can add a setting to the column whether it should round it to nearest integer or not, and with how many decimals.