Move the take over mode to the input implementation

[rdner]

Describe the enhancement:

Currently, the take-over mode used for migrating log inputs to filestream inputs is running before we start any inputs and migrates everything at once for the best possible performance.

We might be able to move this logic to the filestream's prospector when it starts instead. The prospector has access to the state via this interface:

beats/filebeat/input/filestream/internal/input-logfile/prospector.go

Lines 39 to 49 in 7e61ff0

	type StateMetadataUpdater interface {
	// FindCursorMeta retrieves and unpacks the cursor metadata of an entry of the given Source.
	FindCursorMeta(s Source, v interface{}) error
	// UpdateMetadata updates the source metadata of a registry entry of a given Source.
	UpdateMetadata(s Source, v interface{}) error
	// Remove marks a state for deletion of a given Source.
	Remove(s Source) error
	// ResetCursor resets the cursor in the registry and drops previous state
	// updates that are not yet ACKed.
	ResetCursor(s Source, cur interface{}) error
	}

We might want to extend the interface and add the take over function.

This will allow us to support take-over for dynamic use-cases but would most likely affect the performance.

Describe a specific use case for the enhancement or feature:

If we allow dynamic take-over it will allow us to use it in autodiscover and running under elastic-agent.