Adding cosmos-kit tutorial and exercise

[liujun93]

Documentation content update for [hands-on-exercise, 3-cosmjs-adv] and [tutorials, 7-cosmjs]

This PR adding cosmos-kit content in cosmjs section, about how to use cosmos-kit as a wallet adapter in dApps

Change scope

The changes in this Pull Request include (please tick all that apply):

• [ ] Small language/grammar fixes
• [ ] Small content fixes
• [x] Addition of new content
• [ ] Sample code/command updates
• [ ] Platform fixes
• [ ] Other

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