Add integration tests

[rcoy-v]

Changes

• Add initial integration tests around projects and occurrences. Not all existing paths are covered, this is just a starting point.
• Run integration tests in CI.
• Fix potential panic in parsing filter expressions.
• Force Elasticsearch to refresh the respective index when changes happen, so they are immediately reflected. For example, now when a project is created it could be immediately retrieved through the API. Before this could potentially fail if the requests happened fast enough, as the default refresh interval is 1 second.
• Refactor filtering package unit tests to Ginkgo/Gomega, to follow rest of unit tests.

[codecov[bot]]

Codecov Report

Merging #12 (71e8151) into main (2100162) will increase coverage by 1.51%. The diff coverage is 95.45%.

@@            Coverage Diff             @@
##             main      #12      +/-   ##
==========================================
+ Coverage   65.76%   67.27%   +1.51%     
==========================================
  Files           2        2              
  Lines         517      547      +30     
==========================================
+ Hits          340      368      +28     
- Misses        153      154       +1     
- Partials       24       25       +1     

Impacted Files	Coverage Δ
go/v1beta1/storage/filtering/filtering.go	97.75% <94.87%> (-2.25%)	:arrow_down:
go/v1beta1/storage/elasticsearch.go	61.35% <100.00%> (+0.42%)	:arrow_up:

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