Make TsTable always store uppercase "INF" && Fixed the NPE bug when TTL is set to "INF" && Distinguish database model in alter database

Description

As the title said.

This PR has:

[ ] been self-reviewed.
- [ ] concurrent read
- [ ] concurrent write
- [ ] concurrent read and write
[ ] added documentation for new or modified features or behaviors.
[ ] added Javadocs for most classes and all non-trivial methods.
[ ] added or updated version, license, or notice information
[ ] added comments explaining the "why" and the intent of the code wherever would not be obvious for an unfamiliar reader.
[ ] added unit tests or modified existing tests to cover new code paths, ensuring the threshold for code coverage.
[ ] added integration tests.
[ ] been tested in a test IoTDB cluster.