Add support for Wildcard Index

[christophstrobl]

A WildcardIndex is an index that can be used to include all fields or specific ones based a given (wildcard) pattern.

The index can be set up programmatically using WildcardIndex via IndexOperations.

mongoOperations
    .indexOps(User.class)
    .ensureIndex(new WildcardIndex("userMetadata"));

db.user.createIndex({ "userMetadata.$**" : 1 }, {})

The @WildcardIndex annotation allows a declarative index setup and can be added on either a type or property.

If placed on a type that is a root level domain entity (one having an @Document annotation) will advise the index creator to create a wildcard index for it.

@Document
@WildcardIndexed
public class Product {
    ...
}

db.product.createIndex({ "$**" : 1 },{})

The wildcardProjection can be used to specify keys to in-/exclude in the index.

@Document
@WildcardIndexed(wildcardProjection = "{ 'userMetadata.age' : 0 }")
public class User {
    private @Id String id;
    private UserMetadata userMetadata;
}
```javascript
db.user.createIndex(
  { "$**" : 1 },
  { "wildcardProjection" :
    { "userMetadata.age" : 0 }
  }
)

Wildcard indexes can also be expressed by adding the annotation directly to the field.
Please note that wildcardProjection is not allowed on nested paths.

@Document
public class User {
    private @Id String id;

    @WildcardIndexed
    private UserMetadata userMetadata;
}

db.user.createIndex({ "userMetadata.$**" : 1 }, {})

Closes: #3225

[mp911de]

That's merged and polished now.