Reach parity with core tantivy

[petr-tik]

Going through the quickstart guide I noticed, the cli offers 2 field options - int or text, while core tantivy offers text, u64, i64, DateTime, Facet and Bytes.

Most likely this will be the first point of call for new users, who want to check tantivy out.

Going forward, if tantivy-cli wants to stay a real and relevant part of tantivy, we will need to invest in continuous feature parity.

It might be easier if we subsume tantivy-cli/src under bin/tantivy-cli in core tantivy. This will help us check, if new fields are included in cli application as well as extend the API endpoint.

We can also use CI to cross-compile and deploy ready tantivy-cli binaries for people to download and play around with.

[petr-tik]

It looks like some code from the cli can and should be integrated back into core. Example below

https://github.com/tantivy-search/tantivy-cli/blob/develop/src/commands/new.rs#L46-L54

I cannot such restrictions in core tantivy, so this is either irrelevant or needs to be behind an Error value in core