Migrate from REST HTTP to official MongoDB Java Driver (org.mongodb:mongodb-driver-sync)

## Summary

The plugin currently performs CRUD operations against Amazon DocumentDB via its REST API using Kestra's internal HTTP client. Since Amazon DocumentDB is MongoDB-compatible, the correct and AWS-recommended integration path is the official MongoDB Java Driver — `org.mongodb:mongodb-driver-sync` (v5.5.1, released 2025-06-06, 118 versions). Migrating to the driver provides a far richer API (aggregation pipelines, transactions, change streams, typed codec support) and eliminates HTTP-level JSON serialisation entirely.

## Motivation

- Amazon DocumentDB exposes a MongoDB-compatible wire protocol; the MongoDB Java Driver is the client AWS itself recommends in its DocumentDB documentation.
- Raw REST API access to DocumentDB is an unusual integration path that limits available operations to what the REST layer exposes. The native driver unlocks the full MongoDB API surface.
- The MongoDB Java Driver handles connection pooling, TLS/SSL, retries, read preferences, and write concerns out of the box — none of which the current HTTP client implementation handles.
- The driver is extremely actively maintained (118 versions, v5.5.1 in June 2025) and versioned in lockstep with the MongoDB server protocol.

## Context

Current implementation uses `io.kestra.core.http.client.HttpClient` against a DocumentDB REST API endpoint. The migration should replace REST calls with `MongoClient` and `MongoCollection` operations, connecting via the standard MongoDB connection string (`mongodb://...` or `mongodb+srv://...` for DocumentDB).

AWS DocumentDB guide: https://docs.aws.amazon.com/documentdb/latest/developerguide/connect-from-outside-a-vpc.html
MongoDB Java Driver: https://www.mongodb.com/docs/drivers/java/sync/current/

## API Reference

- **Official docs**: https://docs.aws.amazon.com/documentdb/latest/developerguide/developer-guide.html
- **Authentication**: Username/password via connection string, TLS via `tls=true&tlsCAFile=...` parameter
- **Connection string**: `mongodb://:@:27017/?tls=true&...`
- **Driver**: `org.mongodb:mongodb-driver-sync` v5.5.1

## Gradle Dependencies

```groovy
// MongoDB Java Driver (sync) — compatible with Amazon DocumentDB
implementation "org.mongodb:mongodb-driver-sync:5.5.1"
```

## Plugin Structure

- **Repository**: `kestra-io/plugin-documentdb`
- **Namespace**: `io.kestra.plugin.documentdb`
- **Categories**: `DATA`, `CLOUD`

## Suggested Tasks

1. Add `org.mongodb:mongodb-driver-sync` to `build.gradle`; remove any HTTP client dependencies used solely for DocumentDB REST calls
2. Implement a shared `DocumentDbClientFactory` or abstract base task that builds a `MongoClient` from `Property connectionString` (or individual host/port/credentials), handling TLS options for DocumentDB
3. Annotate credentials in the connection string (or `Property password`) with `@PluginProperty(secret = true)`
4. Implement or migrate tasks: `InsertOne`, `InsertMany`, `FindOne`, `Find`, `UpdateOne`, `UpdateMany`, `DeleteOne`, `DeleteMany`, `Aggregate`
5. Support `fetchType` (`FETCH_ONE`, `FETCH`, `STORE`) for read tasks returning data
6. Use `Property` for all properties; model query/pipeline as `Property>`
7. Update unit tests to use a Testcontainers MongoDB instance (compatible with DocumentDB wire protocol) or Wiremock if Testcontainers is unavailable
8. Verify all `@Schema` annotations, Lombok annotations, and logging via `runContext.logger()` are present
9. Update YAML examples and documentation

## YAML Examples

### Example 1 — Insert a document into a DocumentDB collection

```yaml
id: insert_documentdb
namespace: company.team

tasks:
- id: insert
type: io.kestra.plugin.documentdb.Insert
connectionString: "{{ secret('DOCUMENTDB_URI') }}"
database: mydb
collection: events
document:
eventId: "{{ execution.id }}"
status: completed
timestamp: "{{ execution.startDate }}"
```

### Example 2 — Query documents and store results

```yaml
id: query_documentdb
namespace: company.team

tasks:
- id: find_records
type: io.kestra.plugin.documentdb.Find
connectionString: "{{ secret('DOCUMENTDB_URI') }}"
database: mydb
collection: orders
filter:
status: pending
fetchType: STORE

- id: log_count
type: io.kestra.plugin.core.log.Log
message: "Found {{ outputs.find_records.size }} pending orders"
```

### Example 3 — Trigger on new documents inserted into a collection

```yaml
id: react_to_new_document
namespace: company.team

triggers:
- id: on_new_order
type: io.kestra.plugin.documentdb.InsertTrigger
connectionString: "{{ secret('DOCUMENTDB_URI') }}"
database: mydb
collection: orders
filter:
status: new
interval: PT1M

tasks:
- id: process_order
type: io.kestra.plugin.core.log.Log
message: "New order received: {{ trigger.documentId }}"
```

## Acceptance Criteria

### Functional
- [ ] CRUD operations work against a DocumentDB-compatible MongoDB instance
- [ ] TLS/SSL configuration supported via connection string parameters
- [ ] `fetchType` (`FETCH_ONE`, `FETCH`, `STORE`) supported on read tasks
- [ ] Unit tests pass (`./gradlew test`) using Testcontainers or Wiremock
- [ ] Build passes (`./gradlew build`)

### Kestra Plugin Coding Standards
- [ ] All new/refactored properties use `Property`
- [ ] Credentials annotated with `@PluginProperty(secret = true)`
- [ ] Every property and output has a `@Schema` annotation
- [ ] Task classes carry all five mandatory Lombok annotations
- [ ] Logging via `runContext.logger()` only
- [ ] No raw HTTP client dependencies remain for DocumentDB operations

### Documentation
- [ ] `@Plugin(examples = ...)` entries set `full = true` with complete runnable flows
- [ ] Sensitive values in examples use `{{ secret('...') }}`

Start with build.gradle and the existing DocumentDB task implementations to map the REST client usage and shared properties. Review the CRUD and trigger entry points, then run ./gradlew test to understand current coverage. Done means MongoDB-driver operations cover the listed tasks, tests and build pass, and examples and documentation meet the stated acceptance criteria.

Written by the indexing model from the issue text.