[DE-546] Adding stats fields to the explain API

[apetenchea]

Purpose
Enhance the AQL explain functionality by adding the following attributes (available since 3.10.4):

• peakMemoryUsage (number): The maximum memory usage of the query during explain (in bytes)
• executionTime (number): The (wall-clock) time in seconds needed to explain the query.
  Note that the explain method of AQL queries includes the "stats" field in the returned object. The REST API returns it separately from the "plan" field, but for now we have to merge them together to ensure backward compatibility.

Additionally, the following changes are being made

• Adding peak_memory_usage as a new property of AQL queries, available since ArangoDB 3.11
• Adding a CHANGELOG file for keeping track of changes across driver releases

Tests
The necessary tests have been adapted. Note that we have to differentiate now between ArangoDB versions while running the tests.

[codecov-commenter]

Codecov Report

Merging #251 (52648c7) into main (47a0047) will increase coverage by 0.00%.
The diff coverage is 100.00%.

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@@           Coverage Diff           @@
##             main     #251   +/-   ##
=======================================
  Coverage   98.57%   98.57%           
=======================================
  Files          26       26           
  Lines        3853     3858    +5     
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+ Hits         3798     3803    +5     
  Misses         55       55           

Impacted Files	Coverage Δ
arango/aql.py	95.00% <100.00%> (+0.10%)	⬆️
arango/client.py	100.00% <100.00%> (ø)
arango/request.py	94.44% <100.00%> (ø)