Behaviors when specifying dest and output options simultaneously

[filzrev]

#8727 introduce output config for docfx build and docfx pdf commands.
And default docfx seed projects is rewritten using output config. and remove dest config.

When specifying dest and output config simultaneously. (or additionally passing command line parameter with -o)
Output directory is resolved to /{output}/{dest}/ directory.

I thought it should raise error. when both dest and output configs are specified.
And dest config should be marked deprecated by JSON schema. (Thought currently no official json schema exists.)

Additionally, docfx metadata and docfx merge command should support output json config also.