[WIP][spike] feat: build fallback config

[czeslavo]

What this PR does / why we need it:

It's a rough PoC that implements a way to recover from an invalid configuration (in DB-less mode). How it works:

• build a configuration out of the current Kubernetes cache state (current config),
• (optional) detect issues of the built configuration upfront for errors that Kong doesn't catch properly today (e.g. multiple instances of the same plugin type used by a single service/route returns no detailed errors pointing to the affected entities in the flat errors response) - it's not implemented in this PoC.
• try to apply the configuration to Kong,
• Kong rejects the configuration (i.e. there was an error that we weren't able to catch before sending it)
• take the last known good configuration and build an undirected graph from it that reflects relations between entities (every entity is a vertex, and every relation is an edge)
• do the same for the current configuration (the one we know has errors)
• find connected components of both graphs that include the error-affected entities (e.g. if a Plugin has an invalid configuration and it's attached to a Service, we'd get a component consisting of the Plugin, the Service, and Routes attached to the Service)
• build a fallback config by
  • copying the current configuration graph
  • removing the component that includes the affected entity
  • adding the component that includes the affected entity (or any of the entities from the faulty component) from the last known good config (if it was found)
• send the fallback config to Kong and expect success (in the case of failure - fallback to using the last known good config as whole)

Which issue this PR fixes:

Aims to prepare a solution that could solve #2195.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (11cfdb9) 67.9% compared to head (b66ca85) 0.0%.
Report is 391 commits behind head on main.

❗ Current head b66ca85 differs from pull request most recent head b85a741. Consider uploading reports for the commit b85a741 to get more accurate results

Additional details and impacted files

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- Coverage   67.9%       0   -68.0%     
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  Files        164       0     -164     
  Lines      19289       0   -19289     
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- Hits       13107       0   -13107     
+ Misses      5414       0    -5414     
+ Partials     768       0     -768     

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