docs: Ibcv2 callbacks update

[womensrights]

Description

• adds warning that ica is only relevant for use with ibc classic
• updates callbacks integration
• adds in a ibcv2 specific differences page for v2
• had to merge the commits with the ibc v2 middleware section so could reference them in the docs

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[AdityaSripal]

docs/docs/04-middleware/01-callbacks/07-callbacks-IBCv2.md looks fine to me.

I don't understand why you had to merge the previous commits into here and squash them. I think this is why the diffs look so large. Can you just cherry pick the commit you need. Or even simpler just create a new branch off main and copy-paste the new info. In general its best for this PR to only contain the diffs you need

[womensrights]

closed in favour of #8216 for callbacks only without squashed commit