pgAdmin 4 commit: Ensure that the user should not be able to change the

Ensure that the user should not be able to change the authentication source. Fixes #5419
Ensure error should be handled properly when LDAP user is created with the same name. Fixes #5420
Fixed an issue where an internal user is not created if the authentication source is set to internal and ldap. Fixes
#5432

Branch
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master

Details
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https://git.postgresql.org/gitweb?p=pgadmin4.git;a=commitdiff;h=b0464500ca78c535a397a007eb628b5530ce3f19
Author: Khushboo Vashi <khushboo.vashi@enterprisedb.com>

Modified Files
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docs/en_US/release_notes_4_21.rst                  |  5 ++-
web/pgadmin/authenticate/ldap.py                   | 19 +++++----
web/pgadmin/tools/user_management/__init__.py      | 12 +++---
.../user_management/static/js/user_management.js   | 48 +++++++++++++++++-----
4 files changed, 60 insertions(+), 24 deletions(-)