Add v2 demo app with legacy modules

[alpe]

See #1286

[codecov]

Codecov Report

Merging #1287 (1574920) into main (22c77b6) will decrease coverage by 0.18%.
The diff coverage is 81.81%.

@@            Coverage Diff             @@
##             main    #1287      +/-   ##
==========================================
- Coverage   59.46%   59.29%   -0.18%     
==========================================
  Files          57       56       -1     
  Lines        7320     7284      -36     
==========================================
- Hits         4353     4319      -34     
+ Misses       2653     2651       -2     
  Partials      314      314              

Impacted Files	Coverage Δ
app/encoding.go	100.00% <ø> (ø)
app/test_helpers.go	59.70% <50.00%> (ø)
app/app.go	85.68% <100.00%> (-0.60%)	⬇️