V2: Remove headless-ui; replace with radixui

[markphelps]

Headless UI has moved on to v2 and v1 is deprecated

@erka has already taken some of the steps to move some components over to RadixUI here: #3634

We should continue the work to move off of headlessui where possible (where there is a matching component in radixUI

I'd like to propose the following:

1. We do this over several PRs, component by component
2. When updating, we move all shared components to the root ui/components folder (ie: everything in ui/components/ui + ui/components/forms, etc all go into the root ui/components. I think this will help with discoverability, meaning if someone new comes in they will more easily find these existing components instead of trying to implement new ones
3. We ensure the visual styles of the new radix based components match existing components as closely as possible

_FLI-1388

[kartik-raj7]

Hey can i work on this issue

[markphelps]

@kartik-raj7 ty! Assigned to you

[markphelps]

Moving this to be v2 only (v2 branch)

[markphelps]

Remaining headless ui references:

src/components/variants/VariantForm.tsx
1:import { Dialog } from '@headlessui/react';

src/components/forms/Listbox.tsx
1:import { Listbox as L, Transition } from '@headlessui/react';

src/components/panels/DeletePanel.tsx
1:import { Dialog } from '@headlessui/react';

src/components/panels/CopyToNamespacePanel.tsx
1:import { Dialog } from '@headlessui/react';

src/components/Combobox.tsx
1:import { Combobox as C } from '@headlessui/react';

src/components/namespaces/NamespaceForm.tsx
1:import { Dialog } from '@headlessui/react';

src/components/rules/RuleForm.tsx
1:import { Dialog } from '@headlessui/react';

src/components/Sidebar.tsx
1:import { Dialog, Transition } from '@headlessui/react';

src/components/command/CommandDialog.tsx
1:import { Dialog } from '@headlessui/react';

src/components/Slideover.tsx
1:import { Dialog, Transition } from '@headlessui/react';

src/components/Modal.tsx
1:import { Dialog, Transition } from '@headlessui/react';

src/components/rollouts/EditRolloutForm.tsx
1:import { Dialog } from '@headlessui/react';

src/components/rollouts/RolloutForm.tsx
1:import { Dialog } from '@headlessui/react';

src/components/notifications/SuccessNotification.tsx
1:import { Transition } from '@headlessui/react';

src/components/notifications/ErrorNotification.tsx
1:import { Transition } from '@headlessui/react';

src/components/UnsavedChangesModal.tsx
1:import { Dialog } from '@headlessui/react';

src/components/header/Notifications.tsx
1:import { Transition } from '@headlessui/react';

src/components/segments/ConstraintForm.tsx
1:import { Dialog } from '@headlessui/react';