Add reference documentation for beans element 'profile' attribute [SPR-7533]

[spring-projects-issues]

Chris Beams opened SPR-7533 and commented

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This issue is a sub-task of #12165

[spring-projects-issues]

Sam Brannen commented

Already documented:

http://docs.spring.io/spring/docs/current/spring-framework-reference/htmlsingle/#beans-definition-profiles-xml