Re-consider having seq as part of API definition

[vboctor]

Where an API is positioned in a folder isn't really part of the API definition. It would be great if this can be removed from the bru file. Following are some reasons:

1. Removing or adding an API to the top of a list now, will result on all APIs in the folder showing up as updated.
2. Duplicating an API or copying and pasting will require manual revisiting of seq in the newly manually added API file + all other files in the same folder.

It would be great if there is there is a manifest file in the folder that captures folder level properties + ordering of the APIs. If an API file is manually added and is not in the manifest, then the client should add it to the end and update the manifest file.

This reduces the noise on git commits and makes the API files focus on the definition and not the view aspects like the ordering.

The manifest can be the equivalent of a collection definition file or a folder definition file.