Add environment prefix support to SpringApplicationBuilder

Closes gh-25740

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/builder/SpringApplicationBuilder.java

 /*
- * Copyright 2012-2020 the original author or authors.
+ * Copyright 2012-2021 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -534,6 +534,18 @@ public class SpringApplicationBuilder {
 		return this;
 	}
 
+	/**
+	 * Prefix that should be applied when obtaining configuration properties from the
+	 * system environment.
+	 * @param environmentPrefix the environment property prefix to set
+	 * @return the current builder
+	 * @since 2.5.0
+	 */
+	public SpringApplicationBuilder environmentPrefix(String environmentPrefix) {
+		this.application.setEnvironmentPrefix(environmentPrefix);
+		return this;
+	}
+
 	/**
 	 * {@link ResourceLoader} for the application context. If a custom class loader is
 	 * needed, this is where it would be added.

spring-boot-project/spring-boot/src/test/java/org/springframework/boot/builder/SpringApplicationBuilderTests.java

 /*
- * Copyright 2012-2020 the original author or authors.
+ * Copyright 2012-2021 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -291,6 +291,12 @@ class SpringApplicationBuilderTests {
 		assertThat(this.context.getBean("test")).isEqualTo("spring");
 	}
 
+	@Test
+	void setEnvironmentPrefix() {
+		SpringApplicationBuilder builder = new SpringApplicationBuilder(ExampleConfig.class).environmentPrefix("test");
+		assertThat(builder.application().getEnvironmentPrefix()).isEqualTo("test");
+	}
+
 	@Configuration(proxyBeanMethods = false)
 	static class ExampleConfig {