ATLAS-5339: Atlas React UI: Clicking Create Entity while on an Entity Detail Page opens the Edit Form instead of Create Form

[Brijesh619]

What changes were proposed in this pull request?
ATLAS-5339: Fix issue where clicking "Create Entity" from the header dropdown while on an Entity Detail page incorrectly opens the Edit form instead of the Create form.

Root Cause:
When a user is on an Entity Detail page, the URL contains a guid parameter. The EntityForm component automatically reads this guid from the URL parameters (useParams) and assumes the user wants to edit that specific entity.

Fix:

• Added an isAdd boolean prop to the EntityForm component.
• Updated the CreateDropdown component to explicitly pass isAdd={true} when opening the entity form.
• Modified EntityForm to check for isAdd. If isAdd is true, it explicitly ignores the guid from the URL parameters (const guid = isAdd ? undefined : urlGuid;), forcing the form to open in Create mode instead of Edit mode.
• Added unit tests in CreateDropdown.test.tsx to verify the isAdd prop is passed correctly.

How was this patch tested?

• Unit Tests: Added unit tests to CreateDropdown.test.tsx to verify the isAdd state is accurately passed to the EntityForm.
• Test Suite: Ran the full Jest test suite (npm run test:coverage). Verified that all 4,630 tests pass successfully with 0 failures and overall coverage is well above the 50% threshold.
• Manual UI Testing: Navigated to an existing Entity Detail page (where the URL contains a guid), clicked the "Create Entity" button from the header, and verified that a blank Create Form opens instead of the pre-filled Edit Form for the current entity.

[Brijesh619]

[Brijesh619]

[Brijesh619]