fix(admin): refine .mjs related NC28 upgrade info

[MichaIng]

To cover rewrites, Cache-Control header, and give a concrete config file for MIME types, as suggested here: https://github.com/nextcloud/documentation/pull/11471#issuecomment-1912212928

☑️ Resolves

• Fix #11429

🖼️ Screenshots

[kesselb]

Thank you :+1:

[MichaIng]

I am currently building it for a screenshot, just to be sure the nested list looks fine.

EDIT: Now it looks fine:

[st3iny]

/backport to stable28

[st3iny]

/backport to stable29

[backportbot[bot]]

The backport to stable28 failed. Please do this backport manually.

# Switch to the target branch and update it
git checkout stable28
git pull origin stable28

# Create the new backport branch
git checkout -b backport/11912/stable28

# Cherry pick the change from the commit sha1 of the change against the default branch
# This might cause conflicts, resolve them
git cherry-pick 71f8a731

# Push the cherry pick commit to the remote repository and open a pull request
git push origin backport/11912/stable28

Error: No changes found in backport branch

---

Learn more about backports at https://docs.nextcloud.com/server/stable/go.php?to=developer-backports.

[backportbot[bot]]

The backport to stable29 failed. Please do this backport manually.

# Switch to the target branch and update it
git checkout stable29
git pull origin stable29

# Create the new backport branch
git checkout -b backport/11912/stable29

# Cherry pick the change from the commit sha1 of the change against the default branch
# This might cause conflicts, resolve them
git cherry-pick 71f8a731

# Push the cherry pick commit to the remote repository and open a pull request
git push origin backport/11912/stable29

Error: No changes found in backport branch

---

Learn more about backports at https://docs.nextcloud.com/server/stable/go.php?to=developer-backports.

[st3iny]

Damn, need to wait for the other backports ...

[MichaIng]

Makes sense, they are currently blocked by "Block merges during freezes", hence needs someone with more permissions.

[MichaIng]

/backport to stable29

[MichaIng]

/backport to stable28

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