Stalwart Migration Documentation

[simprobe]

The current documentation page for migration (https://stalw.art/docs/management/migration/) does not outline which subspaces map to which store type (Data, Blob, Search, In-Memory). Therefore, if a user wishes to move just the "Data" store, they have to kind of guess and infer what all subspaces are associated. Would recommend adding a column next to the subspace listing in the "Subspace Structure"

I assume the following are the maps:

Blob Store: j, k, t
Search Index: z
In-Memory Store: m, y
Data Store: a, d, f, i, l, n, p, s, e, q, u, h, r, o, x

The clarity would be very much appreciated just for sanity to know how each subspace maps now and in the future.