move demo into workspace

[danieleades]

builds on #117 and adds the demo application to the workspace

once again, i have to stress that this is in no way introducing tight coupling between crates that doesn't already exist, it just means that the tight coupling can be managed by making updates to the demo application in lock-step with the core library it demos.

[codecov]

Codecov Report

Attention: Patch coverage is 86.85714% with 207 lines in your changes missing coverage. Please review.

Project coverage is 86.65%. Comparing base (1a8f6e7) to head (935d756).
Report is 8 commits behind head on main.

Files with missing lines	Patch %	Lines
persistence/postgres-es/src/error.rs	18.60%	35 Missing ⚠️
persistence/mysql-es/src/error.rs	19.04%	34 Missing ⚠️
persistence/mysql-es/src/cqrs.rs	47.27%	29 Missing ⚠️
persistence/postgres-es/src/cqrs.rs	48.21%	29 Missing ⚠️
persistence/mysql-es/src/event_repository.rs	95.80%	18 Missing ⚠️
persistence/postgres-es/src/event_repository.rs	95.73%	18 Missing ⚠️
persistence/mysql-es/src/testing.rs	70.68%	17 Missing ⚠️
persistence/postgres-es/src/testing.rs	70.68%	17 Missing ⚠️
persistence/mysql-es/src/view_repository.rs	94.79%	5 Missing ⚠️
persistence/postgres-es/src/view_repository.rs	95.09%	5 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #121      +/-   ##
==========================================
+ Coverage   84.67%   86.65%   +1.97%     
==========================================
  Files          21       32      +11     
  Lines        2212     3476    +1264     
==========================================
+ Hits         1873     3012    +1139     
- Misses        339      464     +125     

Flag	Coverage Δ
cqrs	84.00% <ø> (?)
mysql	86.91% <86.91%> (?)
postgres	65.15% <86.80%> (?)

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