docs(cosmovisor): update simapp migration example

[fmorency]

Description

Closes: #17582

This PR streamlines the cosmovisor simapp upgrade example to "just work" with the current and previous CosmosSDK versions.

This PR

• removes references to legacy CosmosSDK versions
• fixes genesis voting_period path
• updates the CosmosSDK version used in the example
• clarifies where to find the simdapp migration (name)
• fixes link to the x/upgrade documentation
• clarifies that the migration name given to cosmovisor must match the migration name defined in the migration plan

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[julienrbrt]

utACK. Thank you!