fix: handle dav external storage roots with spaces

[icewind1991]

Allows configuring WebDAV external storage with a space (or other characters that require url encoding) in the "Remote subfolder"

• Make sure the root we work with isn't urlencoded
• Encode the general base url

Fixes #52863

[icewind1991]

/backport to stable31

[provokateurin]

@icewind1991 backport to stable30 as well?

[skjnldsv]

Tests? 🙈

[backportbot]

The backport to stable31 failed. Please do this backport manually.

# Switch to the target branch and update it
git checkout stable31
git pull origin stable31

# Create the new backport branch
git checkout -b backport/53729/stable31

# Cherry pick the change from the commit sha1 of the change against the default branch
# This might cause conflicts, resolve them
git cherry-pick 6d0119bf

# Push the cherry pick commit to the remote repository and open a pull request
git push origin backport/53729/stable31

Error: Failed to push branch backport/53729/stable31: fatal: could not read Username for 'https://github.com': No such device or address

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