FindAndRerank support (collections)

[sl-at-ibm]

No description provided.

[sl-at-ibm]

Ok, @toptobes , this is now ready for a real review. I think we're essentially there.

• If the class naming scheme I shared with you does convince you;
• if we're ok to keeping the actual methods in FindAndRerankOptions and not push them down to CollectionFindAndRerankOptions (methods like RerankOn, etc). I mean, table FARR is not a thing yet and we cannot guess the details of that API -- however, even having to move some/all methods down to collections post-GA, albeit technically "breaking", would practically be a quasi-academic concern I think (and now the arrangement of methods is analogous to the regular-find case)
• A third (minor) point is the choice of calling the three fluent methods of BaseFindAndRerankOptions like this: HybridLimits, VectorLimit/LexicalLimit -- note the plural form for the first only. These names (the latter two) do not appear explicitly in the payload, but I think it makes sense to call them so given the meaning of the short/long forms in the payload. Opinions may vary whether this confuses more/less.

[sl-at-ibm]

Also here some minimal guidance (in part. for @skedwards88 and doc updates if/when this gets merged):

(see CollectionFARRCursorTests.cs for full API demonstration)

var farrFindOptions = new CollectionFindAndRerankOptions<FARRCursorTestVectorDocument> {
    Sort = Builders<FARRCursorTestVectorDocument>.CollectionFindAndRerankSort.Hybrid(new float[] {1.0f, 0.0f}, "blabla"),
    ... // see CollectionFARRCursorTests for the full story...
};

var cur = filledCollection.FindAndRerank(theRegularFilter, farrFindOptions); // Also fluent API, see `Test_CollectionVectorFARR_FluentInterface`
var results = await cur.ToListAsync(); // etc etc

//  now: results[0].Document is document, results[0].Scores is Dictionary<string, float?> (or null if not requested)

Also (probably not for docs since it's useful only for dev):

var myColl = database.GetCollection(
    "my_collection",
    new DatabaseCollectionCommandOptions() { RerankingAPIKey = "AstraCS:...dev-token..." }
);