Use send in RakeTaskExecutorService

What does this MR do and why?

This MR refactors Search::RakeTaskExecutorService#execute to use send because if we keep using the case statement, it will become unmanageable very fast.

Note: I've opened a separate MR so that we can isolate the change that requires a security review. This MR only should be merged after Refactor elastic.rake tasks into a service (!139452 - merged)

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