use internal fetch function of node

[khassel]

related to #2649

With Node >= v18 comes an internal fetch method. This PR centralizes the use of fetch in a new module js/fetch.js and uses the internal fetch function of node instead external node-fetch library if node version >= v18.

[codecov-commenter]

Codecov Report

Merging #2855 (ab7934f) into develop (a4c77f0) will decrease coverage by 0.98%.
The diff coverage is 28.57%.

@@             Coverage Diff             @@
##           develop    #2855      +/-   ##
===========================================
- Coverage    64.80%   63.82%   -0.99%     
===========================================
  Files            8        9       +1     
  Lines          287      293       +6     
===========================================
+ Hits           186      187       +1     
- Misses         101      106       +5     

Impacted Files	Coverage Δ
js/fetch.js	16.66% <16.66%> (ø)
js/server.js	66.21% <100.00%> (ø)

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