Change how chain links are stored

[dadamu]

Description

This PR changes how chain links are stored and allows to query paginated chain links.
Close #480

Checklist

• Targeted PR against correct branch.
• Linked to Github issue with discussion and accepted design OR link to spec that describes this work.
• Wrote unit tests.
• Wrote integration tests (simulation & CLI).
• Updated the documentation.
• Added an entry to the CHANGELOG.md file.
• Re-reviewed Files changed in the Github PR explorer.

[codecov]

Codecov Report

Merging #489 (03f2291) into master (578f794) will increase coverage by 0.25%.
The diff coverage is 78.75%.

@@            Coverage Diff             @@
##           master     #489      +/-   ##
==========================================
+ Coverage   83.74%   83.99%   +0.25%     
==========================================
  Files          91       91              
  Lines        4127     4124       -3     
==========================================
+ Hits         3456     3464       +8     
+ Misses        513      500      -13     
- Partials      158      160       +2     

Impacted Files	Coverage Δ
x/profiles/client/cli/query.go	0.00% <0.00%> (ø)
x/profiles/keeper/keeper.go	86.66% <0.00%> (+5.18%)	⬆️
x/profiles/types/account.go	54.19% <ø> (+2.79%)	⬆️
x/profiles/keeper/alias_functions.go	78.00% <61.11%> (-9.50%)	⬇️
x/profiles/client/cli/cli_chain_links.go	87.01% <77.77%> (-4.77%)	⬇️
x/profiles/keeper/grpc_query.go	75.00% <90.00%> (-1.20%)	⬇️
x/profiles/keeper/genesis.go	81.81% <100.00%> (+3.43%)	⬆️
x/profiles/keeper/keeper_chain_links.go	90.90% <100.00%> (+3.40%)	⬆️
x/profiles/keeper/msg_server_chain_link.go	100.00% <100.00%> (ø)
x/profiles/keeper/relay_chain_links.go	86.66% <100.00%> (ø)
... and 3 more

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[RiccardoM]

Instead of defining a ChainLinkEntry, what I think we can do is simply add the User field to the ChainLink message itself. This should make it more easy to manage, export and import.

[leobragaz]

Looks good to me, only a thing that IMO can be improved

[RiccardoM]

Just a couple of minor improvements