feature: allowing user provided --assembly and --preset

[fboucquez]

Continuation of https://github.com/symbol/symbol-bootstrap/pull/328.

This pr allows users to provide their own network preset and seed folder.

Use cases:

1) We are creating a new testnet network that hasn't been published in bootstrap yet (because it's being created). To create these nodes, we would do:

symbol-bootstrap start --preset new-testnet-network.yml --assembly dual

Once we create the "seed" nodes, we can move new-testnet-network.yml and nemesis block into bootstrap official testnet. Once bootstrap has the new testnet network.yml and seed, it can be released so people can use symbol-bootstrap start --preset testnet --assembly dual to connect to the brand new network.

2) We are creating a new experimental testnet network that will "never" be part of bootstrap, for example, garush.dev:

symbol-bootstrap start --preset garush-network.yml --assembly dual

In this case, we may or may not share the network.yml and nemesis block with the community, depending on if we want community nodes to be connected or not.

In addition, nemesis information is included in all the network.yml files. This allows Symbol-Network to 'clone' an existing configuration that then the network admin can tune, for example, changing the name of the coin, the supply, divisibility, etc. The garush.dev network is a clone of testnet where I changed the network namespace and coin name

[sonarcloud[bot]]

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