Ability to add custom class in tooltip/popover (#32217)

Porting of #31834 to main.

Co-authored-by: XhmikosR <xhmikosr@gmail.com>

js/tests/unit/popover.spec.js

@@ -116,6 +116,22 @@ describe('Popover', () => {
 
       popover.show()
     })
+
+    it('should show a popover with provided custom class', done => {
+      fixtureEl.innerHTML = '<a href="#" title="Popover" data-bs-content="https://twitter.com/getbootstrap" data-bs-custom-class="custom-class">BS twitter</a>'
+
+      const popoverEl = fixtureEl.querySelector('a')
+      const popover = new Popover(popoverEl)
+
+      popoverEl.addEventListener('shown.bs.popover', () => {
+        const tip = document.querySelector('.popover')
+        expect(tip).toBeDefined()
+        expect(tip.classList.contains('custom-class')).toBeTrue()
+        done()
+      })
+
+      popover.show()
+    })
   })
 
   describe('hide', () => {