chore(demo): upgradable realm demo

[mconcat]

Added upgradable realm demo.

• admin: main entrypoint for users and controller contract for store and logic
• store: persistent storage layer across migration steps
• logic: switchable logic implementation

Contributors' checklist...

• Added new tests, or not needed, or not feasible
• Provided an example (e.g. screenshot) to aid review or the PR is self-explanatory
• Updated the official documentation or not needed
• No breaking changes were made, or a BREAKING CHANGE: xxx message was included in the description
• Added references to related issues and PRs
• Provided any useful hints for running manual tests

[dongwon8247]

It's our initial approach to tackle to the upgradable realm feature. Please have a look. @moul @zivkovicmilos @Kouteki

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

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[moul]

We should consolidate all the upgrade demos in one location, and use distinctive names. If you'd like, I can move my other demos to a different folder. Ideally, we should also maintain a shared README that outlines the differences in each implementation; I believe I have already created one.

[dongwon8247]

@moul @mconcat How about we move this PR to https://github.com/gnolang/gno/tree/master/examples/gno.land/r/x/manfred_upgrade_patterns for now as upgrade_g, and share the same README until we reach an agreement on the upgradable pattern for mainnet? Once finalized, we can move the final one to https://github.com/gnolang/gno/tree/master/examples/gno.land/r/demo.

[ltzmaxwell]

LGTM. will approve after this implementation integrated with other ones.

[mconcat]

Moved to manfred_upgrade_patterns folder!