Include path if the base url is generated from the request URL.

[JPBergsma]

This PR fixes a bug in get_base_url.
If the base URL is not specified in the config file, the function get_base_url extracts the base URL from the request URL.
The current function, however, only returns the scheme (e.g. https) and netloc(e.g. www.example.com) part of the base URL.
A base URL may however also contain a root path (e.g. /optimade).
This patch adds the root path to the base URL.

[JPBergsma]

On second thought, I don't think this is needed as it is also possible to set the root_path via a config option.
The root path is not automatically added to the base URL, so a patch for the get_base_url function is still needed.

[codecov]

Codecov Report

Merging #1602 (d0c76cd) into master (8b3e146) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #1602   +/-   ##
=======================================
  Coverage   91.04%   91.05%           
=======================================
  Files          74       74           
  Lines        4578     4583    +5     
=======================================
+ Hits         4168     4173    +5     
  Misses        410      410           

Flag	Coverage Δ
project	91.05% <100.00%> (+<0.01%)	⬆️
validator	90.94% <100.00%> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
optimade/server/routers/utils.py	96.09% <100.00%> (+0.15%)	⬆️

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[JPBergsma]

I just noticed that this PR has a lot in common with PR #663