polish: Fix some inconsistencies in object names and messages

[abh1sar]

Documentation PR for apache/cloudstack#10856

ACL Lists

1. Replace ACL Lists with ACLs as Access Control List Lists doesn't make sense
2. Replace Add ACL with Add ACL rule wherever a rule is being added

User data

1. Following industry conventions, User data should be written as two words
2. The term "User Data" used in the main menu creates some confusion, whether it is singular or plural. So renamed it to "User Data Library" where users can register new User Data.
3. User data should not be followed by "a"

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📚 Documentation preview 📚: https://cloudstack-documentation--506.org.readthedocs.build/en/506/