UserUpdate email already exists error fix

[nitishkumar333]

What kind of change does this PR introduce?
Bugfix

Fixes #1382

Did you add tests for your changes?
Yes

Summary
Added a condition that will check if the user changed the email or not. If the email is changed then only it will check if the email already exists or not. Also changed "find" to "findOne" as we know only one user will have a email and it is faster. Unit test is also added.

Have you read the contributing guide?
Yes

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[nitishkumar333]

@palisadoes added the test also in this PR, by mistake I closed the previous PR so had to open this one.

[codecov]

Codecov Report

Merging #1385 (a36a507) into develop (c0468a4) will increase coverage by 0.06%.
Report is 7 commits behind head on develop.
The diff coverage is 99.69%.

@@             Coverage Diff             @@
##           develop    #1385      +/-   ##
===========================================
+ Coverage    98.17%   98.24%   +0.06%     
===========================================
  Files          184      184              
  Lines        10767    11295     +528     
  Branches       835      874      +39     
===========================================
+ Hits         10571    11097     +526     
- Misses         186      188       +2     
  Partials        10       10              

Files Changed	Coverage Δ
src/resolvers/Mutation/leaveOrganization.ts	98.36% <93.75%> (-1.64%)	⬇️
src/resolvers/DirectChat/organization.ts	100.00% <100.00%> (ø)
src/resolvers/GroupChat/organization.ts	100.00% <100.00%> (ø)
src/resolvers/Mutation/acceptMembershipRequest.ts	100.00% <100.00%> (ø)
src/resolvers/Mutation/addOrganizationImage.ts	100.00% <100.00%> (ø)
src/resolvers/Mutation/addUserToGroupChat.ts	100.00% <100.00%> (ø)
src/resolvers/Mutation/adminRemoveEvent.ts	100.00% <100.00%> (ø)
src/resolvers/Mutation/adminRemoveGroup.ts	100.00% <100.00%> (ø)
src/resolvers/Mutation/blockUser.ts	100.00% <100.00%> (ø)
src/resolvers/Mutation/cancelMembershipRequest.ts	100.00% <100.00%> (ø)
... and 25 more

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[nitishkumar333]

Hi @palisadoes, please give feedback on it.