ci: bump ubuntu version, remove mockldap

[dpgaspar]

Description

• Bump ubuntu base image
• Remove mockldap dependency (still depends on 2to3)
• Migrate LDAP test to integration, run against an openldap container
• bump mongodb dependencies

ADDITIONAL INFORMATION

• Has associated issue:
• Is CRUD MVC related.
• Is Auth, RBAC security related.
• Changes the security db schema.
• Introduces new feature
• Removes existing feature

[codecov]

Codecov Report

Merging #2013 (1425d90) into master (57e9d10) will increase coverage by 0.25%.
The diff coverage is 85.34%.

@@            Coverage Diff             @@
##           master    #2013      +/-   ##
==========================================
+ Coverage   78.10%   78.36%   +0.25%     
==========================================
  Files          71       72       +1     
  Lines        8611     8685      +74     
==========================================
+ Hits         6726     6806      +80     
+ Misses       1885     1879       -6     

Flag	Coverage Δ
python	78.36% <85.34%> (+0.25%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
flask_appbuilder/models/sqla/filters.py	80.11% <50.00%> (-1.33%)	⬇️
flask_appbuilder/fieldwidgets.py	61.01% <59.09%> (-2.15%)	⬇️
flask_appbuilder/security/views.py	65.32% <87.50%> (+2.68%)	⬆️
flask_appbuilder/base.py	84.77% <90.00%> (+0.18%)	⬆️
flask_appbuilder/__init__.py	100.00% <100.00%> (ø)
flask_appbuilder/api/__init__.py	96.34% <100.00%> (+0.03%)	⬆️
flask_appbuilder/baseviews.py	89.90% <100.00%> (+0.25%)	⬆️
flask_appbuilder/security/decorators.py	94.68% <100.00%> (+0.77%)	⬆️
flask_appbuilder/security/manager.py	76.16% <100.00%> (+1.08%)	⬆️
flask_appbuilder/utils/limit.py	100.00% <100.00%> (ø)

... and 3 files with indirect coverage changes

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