Better db migrate error messages

[jedcunningham]

This just cleans up our error messages for db migrate a bit to make them more consistent and intuitive.

e.g. Before:

$ airflow db migrate --show-sql-only  --from-version abc
DB: ...
Traceback (most recent call last):
  File "/home/airflow/.local/bin/airflow", line 8, in <module>
    sys.exit(main())
  File "/home/airflow/.local/lib/python3.8/site-packages/airflow/__main__.py", line 57, in main
    args.func(args)
  File "/home/airflow/.local/lib/python3.8/site-packages/airflow/cli/cli_config.py", line 49, in command
    return func(*args, **kwargs)
  File "/home/airflow/.local/lib/python3.8/site-packages/airflow/utils/cli.py", line 114, in wrapper
    return f(*args, **kwargs)
  File "/home/airflow/.local/lib/python3.8/site-packages/airflow/utils/providers_configuration_loader.py", line 55, in wrapped_function
    return func(*args, **kwargs)
  File "/home/airflow/.local/lib/python3.8/site-packages/airflow/cli/commands/db_command.py", line 111, in migratedb
    if parse_version(args.from_version) < parse_version("2.0.0"):
  File "/home/airflow/.local/lib/python3.8/site-packages/packaging/version.py", line 54, in parse
    return Version(version)
  File "/home/airflow/.local/lib/python3.8/site-packages/packaging/version.py", line 200, in __init__
    raise InvalidVersion(f"Invalid version: '{version}'")
packaging.version.InvalidVersion: Invalid version: 'abc'

After:

$ airflow db migrate --show-sql-only --from-version abc
DB: ...
Invalid version 'abc' supplied as `--from-version`.

and before:

$ airflow db migrate --to-version 2.1.20
DB: ...
Upgrading to version 2.1.20 is not supported.

After:

$ airflow db migrate --to-version 2.1.20
DB: ...
Unknown version '2.1.20' supplied as `--to-version`.