Introduce Spring Session MongoDB

* Migrate the module's code back into this project.
* Fold the documentation in.
* Update to current Gradle conventions.
* Reformat to match styling.

gradle/dependency-management.gradle

@@ -1,6 +1,7 @@
 dependencyManagement {
 	imports {
 		mavenBom 'io.projectreactor:reactor-bom:2020.0.12'
+		mavenBom 'com.fasterxml.jackson:jackson-bom:2.11.2'
 		mavenBom 'org.junit:junit-bom:5.8.1'
 		mavenBom 'org.springframework:spring-framework-bom:5.3.11'
 		mavenBom 'org.springframework.data:spring-data-bom:2021.1.0-RC1'
@@ -15,6 +16,8 @@ dependencyManagement {
 		}
 
 		dependency 'org.aspectj:aspectjweaver:1.9.7'
+		dependency 'ch.qos.logback:logback-core:1.2.3'
+		dependency 'com.google.code.findbugs:jsr305:3.0.2'
 		dependency 'com.h2database:h2:1.4.200'
 		dependency 'com.ibm.db2:jcc:11.5.6.0'
 		dependency 'com.microsoft.sqlserver:mssql-jdbc:9.4.0.jre8'
@@ -28,9 +31,20 @@ dependencyManagement {
 		dependency 'mysql:mysql-connector-java:8.0.26'
 		dependency 'org.apache.derby:derby:10.14.2.0'
 		dependency 'org.assertj:assertj-core:3.21.0'
+		dependency 'org.hamcrest:hamcrest:2.1'
 		dependency 'org.hsqldb:hsqldb:2.5.2'
 		dependency 'org.mariadb.jdbc:mariadb-java-client:2.7.4'
-		dependency 'org.mockito:mockito-core:4.0.0'
+		dependencySet(group: 'org.mockito', version: '4.0.0') {
+        	entry 'mockito-core'
+			entry 'mockito-junit-jupiter'
+		}
+
+		dependencySet(group: 'org.mongodb', version: '4.2.3') {
+			entry 'mongodb-driver-core'
+			entry 'mongodb-driver-sync'
+			entry 'mongodb-driver-reactivestreams'
+		}
 		dependency 'org.postgresql:postgresql:42.2.24'
 	}
 }
+