When unexpected magic bytes occur, improve the feedback in the error shown to the user

[astubbs]

was: Friendlier error when offset decoding fails

When unexpected magic bytes occur, improve the feedback in the error shown to the user.

This can happen when PC is used on a topic, in a CG which had committed something to the metadata which is unexpected. A very rare case, but easy to catch and produce a meaningful error.

Prompted from #326

• On magic byte error, log full metadata
• Common error could be CG reused from KS app - detect KS magic byte and advice as such (inspiration from comment Error in onPartitionsAssigned in parallel consumer #326 )

[astubbs]

We have a slightly friendlier error now - exceptions are caught and context given. But the original suggestions in this ticket should still be done.