Add igx-combo Sample Using `<label igxLabel>` Instead of Placeholder

[georgianastasov]

Description

Add a new sample to the igx-combo documentation showing how to use <label igxLabel> inside the component.

The current igx-combo component overview page uses a placeholder inside the input for labeling, which is not accessible to screen reader users. While the component supports a more accessible method—placing a <label igxLabel> inside <igx-combo>—this approach is undocumented and not shown in examples.

Why Needed

• Placeholders are not announced as labels by screen readers (JAWS, NVDA).
• <label igxLabel> inside <igx-combo> provides proper accessible labeling.
• Without examples, developers are unlikely to discover or implement this more accessible pattern.

Recommendations

Add supporting documentation that explains this method and why it's screen-reader friendly.