[Fix] [connector-hbase] Fix namespace handling for HBase source

[yzeng1618]

Purpose of this pull request

When table is configured as namespace:table, source split enumeration and scan previously used only the table name, effectively querying the default namespace and returning empty results. This PR makes namespace handling consistent across source components and fails fast when table/regions are missing.

Does this PR introduce any user-facing change?

Yes. Reading from non-default namespace tables now returns data correctly instead of 0 rows. The docs also clarify that table accepts namespace:table and defaults to default.

How was this patch tested?

Added/updated unit tests for namespace defaulting and source split enumeration; added an e2e case for namespace source config

Check list

• If any new Jar binary package adding in your PR, please add License Notice according
  New License Guide
• [* ] If necessary, please update the documentation to describe the new feature. https://github.com/apache/seatunnel/tree/dev/docs
• If necessary, please update incompatible-changes.md to describe the incompatibility caused by this PR.
• If you are contributing the connector code, please check that the following files are updated:
  1. Update plugin-mapping.properties and add new connector information in it
  2. Update the pom file of seatunnel-dist
  3. Add ci label in label-scope-conf
  4. Add e2e testcase in seatunnel-e2e
  5. Update connector plugin_config