Fix inconsistent type of visited countries attribute

[Ashesh3]

Related issue: care_fe/issues/2440
Frontend change: care_fe/pull/2536

This change fixes countries_travelled being referenced as a CharField at other places, which causes issues when displaying the data at the frontend.

[vigneshhari]

Need to study the effect of existing null values in FE and BE, otherwise good to go.

[Ashesh3]

@vigneshhari Any updates on this being merged?

[sonarcloud]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
0 Code Smells

No Coverage information
0.0% Duplication

[codecov-commenter]

Codecov Report

Base: 56.08% // Head: 56.08% // Increases project coverage by +0.00% 🎉

Coverage data is based on head (7d8da1d) compared to base (8cbb1c6).
Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #789   +/-   ##
=======================================
  Coverage   56.08%   56.08%           
=======================================
  Files         175      175           
  Lines        8616     8617    +1     
  Branches     1460     1475   +15     
=======================================
+ Hits         4832     4833    +1     
  Misses       3732     3732           
  Partials       52       52           

Impacted Files	Coverage Δ
care/facility/api/serializers/patient_icmr.py	100.00% <100.00%> (ø)
care/facility/api/serializers/patient_sample.py	60.00% <100.00%> (ø)
care/users/api/viewsets/change_password.py	61.53% <0.00%> (+1.53%)	⬆️

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[Ashesh3]

@vigneshhari Any updates on this?