Rework documentation

[lisajulia]

Look at it here:
https://github.com/cap-java/cds-feature-attachments/tree/rework-documentation

Changes:

• major change: changed structure, now we have a "Getting Started" and a "Architecture Overview" section
• changed minimum SAPUI5 Version to 1.139
• added section about multitenancy
• added section about logging
• added sample mta entries for malware scanner and object store

[maxieckert-sap]

One more general remark:

• the documentation uses both, the bookshop sample, as well as the incidents sample app -> let's try to streamline it and use a common sample throughout the docs (i.e. incidents)

[lisajulia]

In capire we would avoid using e.g. and i.e. but I didn't change it here. I'll leave it up to you to replace these with "for example" or "that is" or not.

I've replaced these. Thanks!

[lisajulia]

@renejeglinsky, @eric-pSAP, @maxieckert-sap, @mofterdinger: Can you have yet another look? Thanks!

[renejeglinsky]

Thanks a lot!