Adding support for InsertManyOptions for insert and insertAll methods

[infoShare]

Adding support for InsertManyOptions for insert and insertAll methods on ReactiveMongoTemplate and MongoTemplate
Using writer on MongoTemplate.doInsertAll (which wasn't used)
Closes #4252

• You have read the Spring Data contribution guidelines.
• You use the code formatters provided here and have them applied to your changes. Don’t submit any formatting related changes.
• You submit test cases (unit or integration tests) that back your changes.
• You added yourself as author in the headers of the classes you touched. Amend the date range in the Apache license header if needed. For new types, add the license header (copy from another file and set the current year only).**

Clean PR @christophstrobl regarding #4252

[christophstrobl]

Thanks for creating the PR. Performance wise there is no major difference between the driver API for insertMany and bulk.insert which makes me curious if (related to the missing bulk ops in the reactive support (#2821)) it would make more sense to have ReactiveBulkOperations instead of adding yet another round of methods to the template.
Let me take this to the team as well.

[christophstrobl]

We've added support for reactive bulk operations. Closing this one as it has been superseded by #4342.