Add Path Search Feature to Qlever

[JoBuRo]

This commit adds a feature that computes all paths between pairs of (source, target) on a given graph. The source, target, and graph can be configured. The syntax to trigger this search is using a SERVICE request with a special IRI. The details of this API are described in the file docs/path_search.md.
The current implementation only supports the computation of all paths, which can be exponentially larger than the number of edges in the graph. The implemented infrastructure makes it simpler to implement additional features for this service in the future, such as:

• Only return an arbitrary single path between given start and end nodes.
• Only return the shortest path
• Only return the longest path (same complexity as "all paths" , but less memory requirements).
• Return all edges that lie on an path.

Additionally it can be extended by efficiently supporting the LIMIT/OFFSET clauses and lazy evaluation to efficiently support dealing with very large results in the future.

[JoBuRo]

Current TODOs:

• Implement federated query parsing for path search
• Improve estimates of the PathSearch operation
• Check if building the ResultTable can be improved
• Refactor PathSearch into smaller classes

[codecov]

Codecov Report

Attention: Patch coverage is 90.37657% with 46 lines in your changes missing coverage. Please review.

Project coverage is 88.49%. Comparing base (414f50c) to head (aa632a1).
Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
src/engine/QueryPlanner.cpp	75.34%	11 Missing and 7 partials ⚠️
src/engine/PathSearch.cpp	94.38%	6 Missing and 9 partials ⚠️
src/parser/GraphPatternOperation.cpp	88.88%	5 Missing and 6 partials ⚠️
src/engine/CheckUsePatternTrick.cpp	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1335      +/-   ##
==========================================
+ Coverage   88.39%   88.49%   +0.10%     
==========================================
  Files         362      364       +2     
  Lines       27435    27927     +492     
  Branches     3706     3802      +96     
==========================================
+ Hits        24251    24715     +464     
- Misses       1943     1960      +17     
- Partials     1241     1252      +11     

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[sonarqubecloud]

Quality Gate passed

Issues
17 New issues
0 Accepted issues

Measures
0 Security Hotspots
No data about Coverage
0.0% Duplication on New Code

See analysis details on SonarCloud

[joka921]

Thank you very much, we'll try this out today.

[sparql-conformance]

Conformance check passed ✅

No test result changes.

Details: https://qlever.cs.uni-freiburg.de/sparql-conformance-ui?cur=597a94bf17501d5a2b3031baaa9d131120254101&prev=bf362577394d6b46759c19401ffd6bedb57c7ee7

[sonarqubecloud]

Quality Gate passed

Issues
6 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud