Add a command to add a split file to an existing index.

[fulmicoton]

quickwit add-split --index_uri <index_uri> --split <split_uri> or something like that.

[fmassot]

So with the metastore uri, this will give:

quickwit add-split --index-id <index_id> --split-uri <split_uri> --metastore-uri <metastore_uri>

[guilload]

I have a feeling that in the future, we will want to split the CLI into multiple subcommands/APIs:

quickwit index create/delete/gc/...
quickwit split add/publish/delete/...
quickwit cluster ...