Added ability to change the nav bar height in custom styles

[jones-sam]

This PR adds the ability to change the navbar height when using a custom navbar.

Previously, only the non-custom navbar's height was able to change, while the custom nav was stuck at 56px.

Related to https://github.com/BilalShahid13/PersistentBottomNavBar/issues/160

[amellalalex]

+1

[Fregionz]

Hello, are the ability to change the nav bar height in custom styles added yet?

[sushi86]

+1

Really need this fix!

[realshovanshah]

Same issue here, not really a "highly customizable navbar" without this feature.

[akul1994]

Facing the same issue, requesting a fix please

[koni-ey]

+1 also need this fix 👍

[Vikreddevil]

Please add this !

[ahmadjz]

+1 I really need this fix

[pishguy]

+1