fix: incorrect code generation by swagger-codegen-maven-plugin

[boltaevt]

In case of code generation via swagger-codegen-maven-plugin there are problems with escaping some quote symbols in the sources generated. This causes compilation errors.
The following plugin settings are used for repro:

    <build>
        <plugins>
            <plugin>
                <groupId>io.swagger.codegen.v3</groupId>
                <artifactId>swagger-codegen-maven-plugin</artifactId>
                <version>3.0.41</version>
                <executions>
                    <execution>
                        <goals>
                            <goal>generate</goal>
                        </goals>
                        <configuration>
                            <inputSpec>${project.basedir}/../ewm-main-service-spec.json</inputSpec>
                            <language>spring</language>
                            <library>spring-boot</library>
                            <apiPackage>${apiPackage}</apiPackage>
                            <modelPackage>${modelPackage}</modelPackage>
                            <configOptions>
                                <sourceFolder>src/main/java/</sourceFolder>
                                <dateLibrary>java8</dateLibrary>
                                <interfaceOnly>true</interfaceOnly>
                                <useBeanValidation>true</useBeanValidation>
                                <performBeanValidation>true</performBeanValidation>
                            </configOptions>
                        </configuration>
                    </execution>
                </executions>
            </plugin>
        </plugins>
    </build>

See the whole demo pom.xml in terekhovmv/java-explore-with-me-fixes@da018e0 .

This issue is not reproduced for specs of stats service.