Lazy loading of command table data in interactive.

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-this will allow the completers, which rely on the command_table, to kick in right from the get-go.
-parameter completers will not have to wait for full command table dump.

### Environment summary

Install Method (e.g. pip, interactive script, apt-get, Docker, MSI, edge build) / CLI version (`az --version`) / OS version / Shell Type (e.g. bash, cmd.exe, Bash on Windows)

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