syncthing: Add at 1.29.2

[lz-coder]

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[ermo]

@ikeycode What do we want to do with LICENSE files? Currently, recipes aren't really well aligned:

1. install them to %(datadir)/licenses/%(name)/<the thing> (see f/fdk-aac/stone.yaml)
2. install them to %(docdir)/%(name)/<the thing> (see n/ntpd-rs/stone.yaml)

The present recipe uses the first approach.

Note that FHS 3.0 only specifies %(docdir), not the licenses dir (Section 4.11.3)

Hence, my €0.02 is currently that shoving them in docs for packages is the thing to do.