Create new file rather than overwrite original recipe in `configure_for`/`update_recipe`

Issue #18 / #227 automated the modification of the ESMValTool recipe. The code currently overwrites the original recipe with the modified version.

The code should not do this. It should retain the original file and create a modified version as a new file.

Per this @ehogan comment from the PR:

> I notice that the tests have some additional code to handle that the recipe is being overwritten and I also notice the mv step above. I wonder whether there is a way to have the input (original) recipe and the output (modified) recipe in separate locations so that the additional code from the tests (and potentially the mv above) can be removed?

The mv step being referred to is `=mv ${RECIPE_NAME} ${RECIPE_PATH}`.

To consider: by default, `esmvaltool recipes get ${RECIPE_NAME}` doesn't take a directory argument. From memory (needs checking!) the default save location is `{CYLC_WORKFLOW_SHARE_DIR}` itself - which would possibly be undesirable.

Start by locating the configure_for and update_recipe entry points and the tests that account for the recipe being overwritten; inspect the `mv ${RECIPE_NAME} ${RECIPE_PATH}` step and the `esmvaltool recipes get` behavior. Done means the original recipe is retained, a modified recipe is written separately, and the default output location is resolved and covered by tests.

Written by the indexing model from the issue text.