feat: ADR-010: Mutual DTag exchange between users.

[leobragaz]

Description

This PR implements the changes approved in ADR 010.
Closes: #643

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[codecov]

Codecov Report

Merging #656 (bc9ea35) into master (1a22342) will decrease coverage by 68.53%.
The diff coverage is 55.10%.

@@             Coverage Diff             @@
##           master     #656       +/-   ##
===========================================
- Coverage   84.23%   15.70%   -68.54%     
===========================================
  Files          91      168       +77     
  Lines        6624    45954    +39330     
===========================================
+ Hits         5580     7218     +1638     
- Misses        833    38119    +37286     
- Partials      211      617      +406     

Impacted Files	Coverage Δ
x/profiles/client/cli/cli_app_links.go	34.16% <ø> (ø)
x/profiles/client/cli/cli_params.go	70.00% <ø> (ø)
x/profiles/client/cli/cli_relationships.go	75.51% <ø> (ø)
x/profiles/client/cli/query.go	0.00% <ø> (ø)
x/profiles/client/cli/tx.go	0.00% <ø> (ø)
x/profiles/client/utils/cli.pb.go	3.12% <ø> (ø)
x/profiles/client/utils/utils.go	56.25% <ø> (ø)
x/profiles/keeper/alias_functions.go	90.47% <ø> (ø)
x/profiles/keeper/genesis.go	84.61% <ø> (ø)
x/profiles/keeper/grpc_query.go	73.78% <ø> (ø)
... and 197 more

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[dadamu]

LGTM

[RiccardoM]

Great job! LGTM