Added update_snapshot ext

[zktony]

Describe your changes

1. Added update_snapshot ext.
2. Made submit_snapshot ext feeless.
3. Updated spec_version to 282.

[codecov]

Codecov Report

Base: 53.42% // Head: 53.17% // Decreases project coverage by -0.26% ⚠️

Coverage data is based on head (2a846ba) compared to base (cf5775d).
Patch coverage: 16.66% of modified lines in pull request are covered.

❗ Current head 2a846ba differs from pull request most recent head bccc722. Consider uploading reports for the commit bccc722 to get more accurate results

Additional details and impacted files

@@                 Coverage Diff                 @@
##           mainnet-release     #633      +/-   ##
===================================================
- Coverage            53.42%   53.17%   -0.26%     
===================================================
  Files                   20       20              
  Lines                 1432     1435       +3     
===================================================
- Hits                   765      763       -2     
- Misses                 667      672       +5     

Impacted Files	Coverage Δ
runtime/src/lib.rs	0.00% <ø> (ø)
pallets/ocex/src/lib.rs	73.38% <16.66%> (-0.93%)	⬇️
pallets/asset-handler/src/lib.rs	72.57% <0.00%> (-0.58%)	⬇️

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