fix: update redelegation stringer

[julienrbrt]

Description

Discovered in #14046 that the String() function didn't print all fields.
Ref: #14046 (comment)

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• reviewed API design and naming
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[amaury1093]

Let's add a changelog before merging

[sonarqubecloud]

[Cosmos SDK] Kudos, SonarCloud Quality Gate passed!   

0 Bugs
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100.0% Coverage
0.0% Duplication