[feature] add markdown formatter

[zhangshenghang]

What's changed?

#2518

Support Markdown file formatting

Formatting can be done via spotless apply

At the same time, if it does not meet the specifications during compilation, it will be detected

effect:

Checklist

• I have read the Contributing Guide
• I have written the necessary doc or comment.

@tomsun28 Implemented through the following configuration，

<plugin>
                <groupId>com.diffplug.spotless</groupId>
                <artifactId>spotless-maven-plugin</artifactId>
                <version>2.40.0</version>
                <configuration>
                    <skip>false</skip>
                    <markdown>
                        <includes>
                            <include>home/docs/**/*.md</include>
                        </includes>
                        <flexmark />
                        <replaceRegex>
                            <name>Markdown Formatter</name>
                            <searchRegex>(^-*\n$)([\s\S]*?)(-+$)</searchRegex>
                            <replacement>---$2---</replacement>
                        </replaceRegex>
                    </markdown>
                    <upToDateChecking>
                        <enabled>true</enabled>
                    </upToDateChecking>
                </configuration>
                <executions>
                    <execution>
                        <id>spotless-check</id>
                        <goals>
                            <goal>check</goal>
                        </goals>
                        <phase>validate</phase>
                    </execution>
                </executions>
            </plugin>

[tomsun28]

lgtm!