Add documentation about breaking IOP changes to Helm charts

[Daniel-WWU-IT]

In order for users to be notified about breaking changes in the IOP deployment (e.g., necessary configuration changes), all these changes can easily be added on a per-version basis to the NOTES.txt file of the IOP Helm templates. Thus, after updating their deployment, the user is able to quickly see whether he needs to update a configuration, whether there were any other breaking changes, like new API specs, etc.

An example entry could look like this:

1.10.0:
 - WOPI secret must be specified in the WOPI values file (see <some link here>)