add option to have bundle build write to file, file per instances

[trondhindenes]

In order to integrate with other tools, it would be great if timoni allowed more options in "bundle build", such as outputting to file and splitting up the output so that each instance was placed in its own file.

[stefanprodan]

How should we format the file names? I'm thinking of:

• timoni bundle build --output-dir=./test --output=file-per-instance will generate <instance name>.yaml files
• timoni bundle build --output-dir=./test --output=file-per-resource with generate <kind>_<name>_<index>.yaml files, using the index as a suffix would avoid naming collision.

[trondhindenes]

I think the latter works! Important to avoid collisions, so we'll have to accept slightly convoluted file names