Add missing docs to sov-state

[neysofu]

Description

Add #![missing_docs] to sov-state.

Part of the #438 epic.

[codecov]

Codecov Report

Merging #841 (87af058) into nightly (c2206ff) will increase coverage by 0.0%.
The diff coverage is 96.2%.

Files Changed	Coverage Δ
module-system/sov-state/src/codec/bcs_codec.rs	100.0% <ø> (ø)
module-system/sov-state/src/codec/json_codec.rs	0.0% <0.0%> (ø)
module-system/sov-state/src/codec/split_codec.rs	0.0% <ø> (ø)
module-system/sov-state/src/config.rs	100.0% <ø> (ø)
...e-system/sov-state/src/containers/accessory_map.rs	50.0% <ø> (ø)
module-system/sov-state/src/containers/map.rs	93.6% <ø> (ø)
module-system/sov-state/src/containers/value.rs	69.0% <ø> (ø)
module-system/sov-state/src/lib.rs	81.5% <ø> (ø)
module-system/sov-state/src/scratchpad.rs	95.5% <ø> (ø)
module-system/sov-state/src/storage.rs	97.0% <ø> (ø)
... and 8 more

... and 2 files with indirect coverage changes

[preston-evans98]

This is fantastic, thanks!