Added check for mode to be 'host'/'participant'

[ShauryaAg]

Fixes: #3411

Added check for mode query param in /api/challenges/challenge to be either 'host' or 'participant'

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 69.69%. Comparing base (96968d6) to head (b3a5665). Report is 1162 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3412      +/-   ##
==========================================
- Coverage   72.93%   69.69%   -3.24%     
==========================================
  Files          83       21      -62     
  Lines        5368     3607    -1761     
==========================================
- Hits         3915     2514    -1401     
+ Misses       1453     1093     -360     

see 65 files with indirect coverage changes

see 65 files with indirect coverage changes

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[ShauryaAg]

@Ram81 @RishabhJain2018 Ping for review.