feat(table): Add optional footer row

[ptxmac]

Describe your changes

This adds a .Footer method similar to .Headers.

It will add a final row in the table, which can have its own styling and a border.

I find lipgloss to have prettier defaults than go-pretty, and this adds one of the few missing features I've had moving from go-pretty's table to lipgloss.

Checklist before requesting a review

• I have read CONTRIBUTING.md
• I have performed a self-review of my code

If this is a feature

I'm not sure if this counts as a "feature" requiring a discussion, but let me know if it does

• I have created a discussion
• A project maintainer has approved this feature request. Link to comment:

[NilsJPWerner]

This would be a fantastic addition!