RUST-1826 Use serde attribute to remove empty write concerns

[JamieTsai1024]

Replaced remove_empty_write_concern macro with serde attribute #[serde(skip_serializing_if = "write_concern_is_empty")] to remove empty write concerns before serialization.

Updated structs

Applied the new serde attribute to write_concern fields in the following structs that previously used remove_empty_write_concern:

• TransactionOptions
• DeleteOptions
• AggregateOptions
• CreateIndexOptions
• DropCollectionOptions
• CreateCollectionOptions
• DropDatabaseOptions
• FindAndModifyOptions
• DropIndexOptions

Also updated additional structs with write_concern fields that serialized empty values before:

• BulkWriteOptions
• InsertOneOptions
• ReplaceOptions
• FindOneAndDeleteOptions
• FindOneAndReplaceOptions
• FindOneAndUpdateOptions

Special cases
Certains structs with write_concern fields do not use the serde attribute for one of the following reasons:

• Fields are added manually only if not empty
  • E.x. UpdateOptions
• The struct itself does not implement serialization (Serialize)
  • E.x. CollectionOrDatabaseOptions, DatabaseOptions, GridFsBucketOptions, AbortTransaction

[isabelatkinson]

Code changes look great! There are just a few CI issues to address:

• The check-cargo-deny and compile-on-msrv tasks can both be fixed by merging with the latest commits on main
• The check-rustfmt lint can be fixed by running rustfmt +nightly --unstable-features src/**/*.rs

[isabelatkinson]

nice work!