Minor change to fallback server.cfg

[ml-evs]

As outlined in a comment in (#119 (comment)), this PR modifies the construction of server.cfg if it's missing. Instead of using server_template.cfg, the created server.cfg uses the absolute paths of the default values for index_links and config.

[codecov]

Codecov Report

Merging #125 into master will increase coverage by 0.01%.
The diff coverage is 90%.

@@            Coverage Diff             @@
##           master     #125      +/-   ##
==========================================
+ Coverage   82.73%   82.75%   +0.01%     
==========================================
  Files          39       39              
  Lines        1813     1815       +2     
==========================================
+ Hits         1500     1502       +2     
  Misses        313      313

Flag	Coverage Δ
#unittests	82.75% <90%> (+0.01%)	⬆️

Impacted Files	Coverage Δ
optimade/server/config.py	77.1% <90%> (+0.56%)	⬆️

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[CasperWA]

Yeah, I found this error in my own server as well, but fixed it there.

This is better, although I don't see why we can't just delete server_template.cfg now?

[ml-evs]

Yeah, I found this error in my own server as well, but fixed it there.

This is better, although I don't see why we can't just delete server_template.cfg

Agreed and done.

[CasperWA]

Thanks for the quickfix @ml-evs !