chore: update cosmos sdk to 0.50.12

[amimart]

Purpose of Changes and their Description

Bump Cosmos SDK version to v0.50.12, it contains a security fix related to the x/group module. We don't use this module so we're not impacted but I propose make this update even if not critical for us.

I've taken the opportunity to rearrange the changelog please let me know if this is the expected format:

• Move the Released flag before the last v0.9.0 version;
• Put this change under the Unreleased elements;

Link(s) to Ticket(s) or Issue(s) resolved by this PR

https://linear.app/alloralabs/issue/ENGN-3484/fix-cosmos-ghsa-x5vx-95h7-rv4p-vulnerability

Are these changes tested and documented?

• If tested, please describe how. If not, why tests are not needed.
• If documented, please describe where. If not, describe why docs are not needed.
• Added to Unreleased section of CHANGELOG.md?

[amimart]

Closing this one if favour of #767