Add information about /liquibase and /flyway to Actuator's docs

Closes gh-3438

spring-boot-actuator-docs/pom.xml

@@ -30,6 +30,10 @@
 			<artifactId>spring-boot-actuator</artifactId>
 			<scope>provided</scope>
 		</dependency>
+		<dependency>
+			<groupId>com.h2database</groupId>
+			<artifactId>h2</artifactId>
+		</dependency>
 		<dependency>
 			<groupId>junit</groupId>
 			<artifactId>junit</artifactId>
@@ -40,6 +44,21 @@
 			<artifactId>groovy-templates</artifactId>
 			<scope>provided</scope>
 		</dependency>
+		<dependency>
+			<groupId>org.flywaydb</groupId>
+			<artifactId>flyway-core</artifactId>
+			<scope>provided</scope>
+		</dependency>
+		<dependency>
+			<groupId>org.liquibase</groupId>
+			<artifactId>liquibase-core</artifactId>
+			<scope>provided</scope>
+		</dependency>
+		<dependency>
+			<groupId>org.springframework</groupId>
+			<artifactId>spring-jdbc</artifactId>
+			<scope>provided</scope>
+		</dependency>
 		<dependency>
 			<groupId>org.springframework</groupId>
 			<artifactId>spring-test</artifactId>

spring-boot-actuator-docs/src/main/asciidoc/flyway.adoc

+=== /flyway
+This endpoint provides information about database migrations that have been performed
+by Flyway.
+
+Example curl request:
+include::{generated}/flyway/curl-request.adoc[]
+
+Example HTTP request:
+include::{generated}/flyway/http-request.adoc[]
+
+Example HTTP response:
+include::{generated}/flyway/http-response.adoc[]

spring-boot-actuator-docs/src/main/asciidoc/liquibase.adoc

+=== /liquibase
+This endpoint provides information about database migrations that have been performed
+by Liquibase.
+
+Example curl request:
+include::{generated}/liquibase/curl-request.adoc[]
+
+Example HTTP request:
+include::{generated}/liquibase/http-request.adoc[]
+
+Example HTTP response:
+include::{generated}/liquibase/http-response.adoc[]

spring-boot-actuator-docs/src/restdoc/resources/db/changelog/db.changelog-master.yaml

+databaseChangeLog:
+  - changeSet:
+      id: 1
+      author: awilkinson
+      changes: