Escape user input in handlers flagged during code scans

[kevin-bates]

This change runs user-input received as an argument on a few handlers through url_escape. These instances had been flagged by the code analysis CI.

Resolves #447

[codecov-io]

Codecov Report

Merging #449 (8a03e48) into master (d690965) will increase coverage by 0.04%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #449      +/-   ##
==========================================
+ Coverage   77.77%   77.81%   +0.04%     
==========================================
  Files         106      106              
  Lines        9089     9089              
  Branches      969      969              
==========================================
+ Hits         7069     7073       +4     
+ Misses       1671     1669       -2     
+ Partials      349      347       -2     

Impacted Files	Coverage Δ
jupyter_server/services/kernels/kernelmanager.py	81.10% <0.00%> (+0.78%)	⬆️
jupyter_server/tests/services/kernels/test_api.py	99.01% <0.00%> (+1.96%)	⬆️

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[blink1073]

Thanks!