[Node operation] Allow private keys to loaded from a different directory than the genesis data

Instructions

Reported by Anchorage

Please fill out the template below to the best of your ability and include a label indicating which tool/service you were working with when you encountered the problem.

Issue To Be Solved

Currently, a Flow node expects a bootstrap directory where it finds the private keys and the genesis data both. The private keys cannot be kept separate than the genesis data in a different folder.
The Flow node should allow for specifying the private keys and genesis data folder separately to allow for easier key management.

(Optional): Suggest A Solution

(Replace This Text: A concise description of your preferred solution. Things to address include:

• Details of the technical implementation
• Tradeoffs made in design decisions
• Caveats and considerations for the future

If there are multiple solutions, please present each one separately. Save comparisons for the very end.)

(Optional): Context

<what are you currently working on that this is blocking?>

Start by locating the Flow node startup and configuration handling for the bootstrap directory. Trace how private keys and genesis data are loaded, then determine where separate locations can be specified. Done means a node can configure distinct directories for private keys and genesis data, with coverage for the separate-path behavior.