docs: Updated migration docs for v13 release

[mmulji-ic]

Description

Part of epic #2741

Updated docs for v13 release.

Author Checklist

All items are required. Please add a note to the item if the item is not applicable and
please add links to any relevant follow up issues.

I have...

• included the correct docs: prefix in the PR title
• targeted the correct branch (see PR Targeting)
• provided a link to the relevant issue or specification
• reviewed "Files changed" and left comments if necessary
• confirmed all CI checks have passed

Reviewers Checklist

All items are required. Please add a note if the item is not applicable and please add
your handle next to the items reviewed if you only reviewed selected items.

I have...

• Confirmed the correct docs: prefix in the PR title
• Confirmed all author checklist items have been addressed
• Confirmed that this PR only changes documentation
• Reviewed content for consistency
• Reviewed content for thoroughness
• Reviewed content for spelling and grammar
• Tested instructions (if applicable)

[mpoke]

LGTM

@mmulji-ic could we move from keeping historical upgrading docs, as they're all quite similar and instead use ./UPGRADING.md when cutting a new release?

[yaruwangway]

The cosmovisor tutorial might be slightly different now.

[mmulji-ic]

LGTM

@mmulji-ic could we move from keeping historical upgrading docs, as they're all quite similar and instead use ./UPGRADING.md when cutting a new release?

I want to start updating content remove duplication after the docusaurus migration.

[sainoe]

LGTM!

[mmulji-ic]

The cosmovisor tutorial might be slightly different now.

We used effectively the same tutorial for the last upgrade, so hopefully its also good this time around. For future releases we want to streamline this totally, as theres a lot of repeated material and its easy for maintainers to make mistakes.