Add various ADRs about the use of state machines

[ehuelsmann]

Before merging:

• Remove empty enumerations

[neilt]

One of the things that might help newcomers to LedgerSMB would be a link to the PR for some code that shows how the implementation was done in LSMB. That might be the first implementation, if it was done right the first time, or a later implementation, if it serves as a better example.

In this case, implementation means how existing code was changed to utilize robot3 or how a new view or component was implemented using robot3.

Rather than have a status date of 'Unknown' which provides no useful implementation, how about considering 'Prior to 4 Dec 2023' or a less specific guess, like '2009'. Another example 'between 2014 and 2015', or with 'LSMB release 1.6'. Any way that we can get more context is good. Right now it does not matter, but this will provide better insight in 10 years.

[freelock]

Some thoughts...

[ehuelsmann]

Added @neilt's suggestion in a new issue.