Deploy 0.40 docs on "/"

[amaury1093]

Summary

Deploy 0.40 docs on the root of https://docs.cosmos.network

Problem Definition

Since docs are still in progress (see epic in #6953), they are not published on the default docs.cosmos.network, but under /master.

Proposal

• The last entry in https://github.com/cosmos/cosmos-sdk/blob/master/docs/versions is the version on /, make sure to point it to an 0.40 branch/tag
• The deprecation URL points to master, make sure to point to / or /v0.40

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For Admin Use

• Not duplicate issue
• Appropriate labels applied
• Appropriate contributors tagged
• Contributor assigned/self-assigned

[clevinson]

This is done in #8285, but currently CI is still failing so not actually deployed

[amaury1093]

done in #8353 for 0.41. Closing this.