What

This MR adds method for executing FA deposits that is supposed to be used by the kernel.

Why

Putting execution logic in FA bridge sub-crate allows to encapsulate business logic and provide a concise integration point.

This MR does not introduce breaking changes nor affects the kernel execution flow.

make test

Document the interface of any function added or modified (see the coding guidelines)
Document any change to the user interface, including configuration parameters (see node configuration)
Provide automatic testing (see the testing guide).
For new features and bug fixes, add an item in the appropriate changelog (docs/protocols/alpha.rst for the protocol and the environment, CHANGES.rst at the root of the repository for everything else).
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