Add description under flag name with tooltip

[zackcl]

Resolves #1704

This PR displays the description under flag name with a tooltip when the text is truncated (for both the name and description) just like how it works on the Experiments root page.

[RidhamShah]

@zackcl This works fine, but I also noticed that in Experiment we also provide a tooltip for Table-Header (Name, Status, Tags ... ) but it is not there for FeatureFlags. Can you add that too?

[zackcl]

@RidhamShah Why do we need to show a tooltip for table headers? I don't think we need to display the tooltip if we are just showing the same text as the headers. But please let me know if you have any specific suggestions for different tooltip messages for the headers.

[RidhamShah]

@RidhamShah Why do we need to show a tooltip for table headers? I don't think we need to display the tooltip if we are just showing the same text as the headers. But please let me know if you have any specific suggestions for different tooltip messages for the headers.

True, but i think we should make it consistent between Experiment, FeatureFlags & Segments

[zackcl]

@RidhamShah Currently, nothing is supposed to be consistent between Feature Flags and other pages since it's a new design. We decided to apply the new design one page at a time, so there may be inconsistencies, but eventually they will be consistent.

[bcb37]

The positioning of the tooltip seems confusing. It appears to cover up the name that the description corresponds to, rather than showing up under the name:

[zackcl]

@bcb37 I tried different positioning, but displaying a tooltip above an element seemed most natural to me. It ends up covering other elements even with different positioning anyway. Also, the user can slightly move the cursor to see the name when it's covered.