FF: Implement Duplicate Feature Flag

[danoswaltCL]

Implement the Duplicate Feature Flag modal.

• Selected from the root page menu
• The Name and Key should be appended with _COPY (or something?) as the suffix when prefilling the form values with the source flag's details (the user is expected to change this).
• This will otherwise work the same as the EDIT flow for pre-filling the details, and will call the same endpoint as ADD.
• As such, it may behoove us to consolidate these 3 states, add edit and duplicate, as one template modal called something like 'Feature Flag Details Modal'.

[danoswaltCL]

(I assigned myself since I already started this work, but we should properly refine it)

[Yagnik56]

@danoswaltCL the name and key aren't appended with _COPY as the suffix instead they are empty when we open the duplicate feature flag modal, did we change it or this is a bug?