Make command-line tools accept minor I/O version numbers as well.

We've added support for requesting a specific major I/O schema version to various tools, such as `kcidb-schema`, `kcidb-validate` and so on, a while ago. That was done when we had separate objects for major versions only. Now we have separate objects for minor versions as well. Make the tool accept a version string as well (as handled by `kcidb.misc.version()` argument type, e.g. `v4.1`), and outputting the corresponding version of the I/O schema. However, make it still accept just the sole major version number and output the latest minor version with the specified major number (as it was done before). This would involve modifying the `kcidb.misc.argparse_schema_add_args()` function.

Start by inspecting kcidb.misc.argparse_schema_add_args() and its callers in tools such as kcidb-schema and kcidb-validate. Check how kcidb.misc.version() parses v4.1, then verify that an exact major.minor selects that I/O schema version while a major-only argument still selects the latest minor version for that major.

Written by the indexing model from the issue text.