Add test for external blog + add alumni login backend

[dev9318]

• Add a test for external blog with SONIC search (done to increase coverage)

[codecov[bot]]

Codecov Report

Merging #468 (6c74b22) into master (2be1053) will increase coverage by 0.04%. The diff coverage is 100.00%.

@@             Coverage Diff             @@
##           master      #468      +/-   ##
===========================================
+ Coverage   99.95%   100.00%   +0.04%     
===========================================
  Files         120       131      +11     
  Lines        4571      5040     +469     
===========================================
+ Hits         4569      5040     +471     
+ Misses          2         0       -2     

Impacted Files	Coverage Δ
backend/urls.py	100.00% <ø> (ø)
login/urls.py	100.00% <ø> (ø)
achievements/admin.py	100.00% <100.00%> (ø)
achievements/models.py	100.00% <100.00%> (ø)
achievements/serializers.py	100.00% <100.00%> (ø)
achievements/tests.py	100.00% <100.00%> (ø)
achievements/urls.py	100.00% <100.00%> (ø)
achievements/views.py	100.00% <100.00%> (ø)
alumni/admin.py	100.00% <100.00%> (ø)
alumni/apps.py	100.00% <100.00%> (ø)
... and 21 more

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