Update asset FT and DEX docs with the extension.

[dzmitryhil]

Description

Update asset FT and DEX docs with the extension.

Reviewers checklist:

• Try to write more meaningful comments with clear actions to be taken.
• Nit-picking should be unblocking. Focus on core issues.

Authors checklist

• Provide a concise and meaningful description
• Review the code yourself first, before making the PR.
• Annotate your PR in places that require explanation.
• Think and try to split the PR to smaller PR if it is big.

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This change is 

[masihyeganeh]

Reviewed 2 of 2 files at r1, all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @miladz68 and @ysv)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 62.44%. Comparing base (43cac5a) to head (32b3a5c).
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1045      +/-   ##
==========================================
+ Coverage   52.55%   62.44%   +9.89%     
==========================================
  Files         142      160      +18     
  Lines       16312    18590    +2278     
==========================================
+ Hits         8572    11609    +3037     
+ Misses       6618     5863     -755     
+ Partials     1122     1118       -4     

Flag	Coverage Δ
coreum	57.10% <ø> (?)
coreum-integration-tests-modules	52.55% <ø> (ø)

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[masihyeganeh]

Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @miladz68 and @ysv)

[miladz68]

Reviewed 2 of 2 files at r1, all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @ysv)