fix: cannot change the state if it's the only state in group

[Palanikannan1437]

• Closes #1329

Issue in brief

Though an user cannot delete the only state of a group, one could change the group of that state by using the dropdown menu.

Suggested Fixes/Changes

• Check if groupLength is 1 (to see it's the only state in the group
• Disable the Dropdown if groupLength is 1
• Add a tooltip to suggest why the DropDown is disabled and the action to perform when it's enabled

Updated screenshots of the above Suggested Changes

• If only one state in the group

• If multiple states present in the group

Demo Time

Before

https://github.com/makeplane/plane/assets/73993394/0a86f0f0-a5cf-415f-8180-eb0971e5cf55

After

https://github.com/makeplane/plane/assets/73993394/8a939b45-d18c-4ce2-bdf1-98558cb35565

Potential Further Steps

• Enforce this login on the backend as well

Updated screenshots of the above after feedback

• Muted dropdown text when disabled

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[Palanikannan1437]

@aaryan610 Would love your feedback on this, thank you!

PS: I'll squash the commits once all the necessary changes are made before the merge, thanks