Fix and refactor error handling in rest catalog

[gabeiglio]

Rationale for this change

Error handling differed with the Java implementation in the following:

• 404 errors for tables or view can be NoSuchNamespaceError if the namespace does not exists (same as Java)
• table commit will use the table error handler (instead of the commit error handler) if the commit will create a table (staged create)
• Created ViewAlreadyExistsError for completeness even though we don't support creating views atm
• Additionally this PR marks commit 503 errors as CommitStateUnkown as changed recently in Java

Are these changes tested?

Added two unit tests for testing the exception thrown between NoSuchNamespaceError and NoSuchTableError

Are there any user-facing changes?

No