added architecture design record for enums

[riederm]

No description provided.

[riederm]

comment from @ghaith: add example with custom numerical type for the enum

[riederm]

comment from @ghaith: add example with custom numerical type for the enum

introduced an examplary case with BYTE as the enum's type (in enums_constants_are_automatically_numbered_or_user_defined)

[codecov-commenter]

Codecov Report

Merging #496 (848fbaf) into master (a0f967e) will increase coverage by 0.05%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #496      +/-   ##
==========================================
+ Coverage   92.89%   92.95%   +0.05%     
==========================================
  Files          39       40       +1     
  Lines       14297    14415     +118     
==========================================
+ Hits        13281    13399     +118     
  Misses       1016     1016              

Impacted Files	Coverage Δ
src/tests/adr/pou_adr.rs	100.00% <ø> (ø)
src/tests/adr/enum_adr.rs	100.00% <100.00%> (ø)

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