Update migration_sdf.md

[EnzoGhisoni]

🦟 Bug fix

Fix #1230
Fix broken links for ERB, Server configuration tutorial and GUI configuration tutorial. These links where pointing to the wrong url, change them to point on .md files related.

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➡️ Forward port

Branch comparison: https:/gazebosim//compare/EnzoGhisoni:gz-sim:patch-1

Note to maintainers: Remember to Merge with commit (not squash-merge or rebase)

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🎈 Release

Preparation for <X.Y.Z> release.

Comparison to <x.y.z>: https:/gazebosim//compare/<LATEST_TAG_BRANCH>...<RELEASE_BRANCH>

Needed by <PR(s)>

Checklist

• Asked team if this is a good time for a release
• There are no changes to be ported from the previous major version
• No PRs targeted at this major version are close to getting in
• Bumped minor for new features, patch for bug fixes
• Updated changelog
• Updated migration guide (as needed)
• Link to PR updating dependency versions in appropriate repository in gazebo-release (as needed):

Note to maintainers: Remember to use Squash-Merge and edit the commit message to match the pull request summary while retaining Signed-off-by messages.

[EnzoGhisoni]

Related to issue gazebosim/gazebo_test_cases#1230 (comment)