Adding --> Add for the object storage

[andrijapanicsb]

Link inside the ACS UI points to:

http://docs.cloudstack.apache.org/en/latest/installguide/configuration.html#add-object-storage

i.e. use word "add" not "adding" - easier to fix docs than the UI.

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📚 Documentation preview 📚: https://cloudstack-documentation--389.org.readthedocs.build/en/389/