Improving docs for DIA

[je-l]

I'd like to overhaul the DIA-related docs, as it's currently slightly vague and even misleading. I feel that a manual-like, objective description which explains how DIA exactly influences the algorithm would be useful.

Also:

• Safety aspects
• Role of zero temping
• Explain how consistent adjustments can be applied by adjusting DIA and peak in parallel
• Interaction of DIA with other AAPS settings

Since AAPS v4 is probably released soon, I figured to write this with v4 in mind.

Any feedback before I open a PR? cc @psonnera

[psonnera]

@je-l please PR in https://github.com/openaps/AndroidAPSdocs/tree/v4 as the current versions is better frozen to help next version merge. Make sure the indications are in agreement with the community guidelines (Loop & Learn). Thanks!