Bump to v0.5.0

[CasperWA]

Highlight:

• Close AiiDA SQLA sessions after an endpoint has collected its data from the AiiDA database (Update session handling per request as per new AiiDA PR 3708 #34).
  This fixes the issue of the QueuePool being filled up, since the connections were never released.

Changes:

• Add optimade-python-tools version to Dockerfile (Add OPTiMaDe Python tools version to docker #45)
• aiida-core version compatibility badge (Add AiiDA version dependency badge #46)
• Use versioned base URLs for endpoint prefixes (Introduce versioned base URLs #51)
• Further minimize code-reproduction and reuse code from optimade (Introduce versioned base URLs #51)
• Use RedirectSlashedURLs from optimade (Introduce versioned base URLs #51)
• Move mapper aliases to config.json file (Introduce versioned base URLs #51)
• Subclass ResourceMapper from optimade and incorporate new REQUIRED levels from the spec (Use ResourceMapper from optimade #52)

[codecov]

Codecov Report

Merging #53 into develop will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff            @@
##           develop      #53   +/-   ##
========================================
  Coverage    69.34%   69.34%           
========================================
  Files           15       15           
  Lines          809      809           
========================================
  Hits           561      561           
  Misses         248      248

Flag	Coverage Δ
#unittests	69.34% <ø> (ø)	⬆️

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