Change flyway/example to flyway/app

[rekjuh]

Change suggested long ago in Oskari-documentation/HowToModifyAppSetups.md

[ZakarFin]

Unfortunate timing with the release just yesterday. But a good change for the next version that might be 3.0

[jampukka]

Checksum comparison will cause error on second run, no?

[ZakarFin]

Checksum comparison will cause error on second run, no?

That is true, but we have also done this in the past as this is a starting point/template for a customized app and not something that is meant to be updated from as such when updating the app: https://github.com/oskariorg/sample-server-extension/blob/master/README.md?plain=1#L53

Having the app specific migrations to be in a more generic "app" module makes sense since the developer can just tinker around with the current starting migrations instead of first renaming the package they are in (from example to something more appropriate for the customised app).

[ZakarFin]

Let's change this for 3.0 just to be sure