Replace template string {resource_dir} in kernelspec

[mlhenderson]

This is an alternate pull request to #818, which added a resource_dir field to the response output. Instead, this PR replaces the template string of {resource_dir} with the provided resource_dir path string, if one exists.

[codecov-commenter]

Codecov Report

Merging #932 (67edba9) into main (0c22000) will decrease coverage by 0.02%. The diff coverage is 94.73%.

@@            Coverage Diff             @@
##             main     #932      +/-   ##
==========================================
- Coverage   72.33%   72.31%   -0.03%     
==========================================
  Files          65       65              
  Lines        7997     8015      +18     
  Branches     1335     1338       +3     
==========================================
+ Hits         5785     5796      +11     
- Misses       1803     1811       +8     
+ Partials      409      408       -1     

Impacted Files	Coverage Δ
jupyter_server/services/kernelspecs/handlers.py	91.89% <91.66%> (-0.05%)	:arrow_down:
jupyter_server/pytest_plugin.py	88.54% <100.00%> (+0.31%)	:arrow_up:
jupyter_server/services/kernels/kernelmanager.py	78.64% <0.00%> (-1.95%)	:arrow_down:

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