refactor: removed disable eslint and created channels constant

[awais-ansari]

INF-1120

• Removed extra spaces from notification preferences module messages.
• Removed disable eslint and refactored code accordingly.
• Create a constant for notification channels and use it accordingly.

[codecov]

Codecov Report

All modified lines are covered by tests ✅

Comparison is base (966b59b) 46.44% compared to head (f866771) 46.46%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #912      +/-   ##
==========================================
+ Coverage   46.44%   46.46%   +0.02%     
==========================================
  Files         116      117       +1     
  Lines        2405     2406       +1     
  Branches      640      640              
==========================================
+ Hits         1117     1118       +1     
  Misses       1214     1214              
  Partials       74       74              

Files	Coverage Δ
...c/notification-preferences/NotificationCourses.jsx	94.73% <ø> (ø)
...fication-preferences/NotificationPreferenceApp.jsx	86.66% <ø> (ø)
...fication-preferences/NotificationPreferenceRow.jsx	88.23% <ø> (ø)
...tification-preferences/NotificationPreferences.jsx	95.83% <100.00%> (ø)
src/notification-preferences/data/constants.js	100.00% <100.00%> (ø)
src/notification-preferences/messages.js	100.00% <100.00%> (ø)

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