Convert demo db tests to e2e tests

[rfdavid]

This PR replaces demo_db_test.cpp by end to end test. It also enables using ${KUZU_ROOT_DIRECTORY} inside .test on query or result lines:

Example:

-QUERY COPY Follows FROM "${KUZU_ROOT_DIRECTORY}/dataset/demo-db/csv/follows.csv"
---- error
Copy exception: COPY commands can only be executed once on a table.

[codecov]

Codecov Report

Patch coverage: 100.00% and no project coverage change.

Comparison is base (da75c9d) 91.86% compared to head (47426ad) 91.86%.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1574   +/-   ##
=======================================
  Coverage   91.86%   91.86%           
=======================================
  Files         701      701           
  Lines       25321    25325    +4     
=======================================
+ Hits        23262    23266    +4     
  Misses       2059     2059           

Impacted Files	Coverage Δ
src/include/common/string_utils.h	100.00% <ø> (ø)
src/common/string_utils.cpp	71.42% <100.00%> (+6.72%)	⬆️

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