Handle private channel hop hints

[contrun]

This PR depends on Use the fee rate in oubound channel to calculate the TLC fee by contrun · Pull Request #489 · nervosnetwork/fiber.

The migration code is not well-tested. I only tried the following.

1. Run git checkout v0.3.1 to checkout to the v0.3.1 version code.
2. Run REMOVE_OLD_STATE=y ./tests/nodes/start.sh to start a few fnn nodes with all new states.
3. Run (cd ./tests/bruno; npm exec -- @usebruno/[email protected] run e2e/router-pay -r --env test) to create a few payment sessions.
4. Run ldb --db=tests/nodes/1/fiber/store --secondary_path=/tmp/test/ dump --hex | awk '/0xC0/ {print $1}' | sed 's/0xC0/0x/g' to see all the payment sessions created.
5. Run ldb --db=tests/nodes/1/fiber/store --secondary_path=/tmp/test/ dump --hex | awk '/0xC0/ {print $1}' | sed 's/0xC0/0x/g' | xargs -I __ curl -sS --json '{"id": "42", "jsonrpc": "2.0", "method": "get_payment", "params": [{"payment_hash": "__"}]}' http://127.0.0.1:21714/ | jq -s to see all the payment session detailed information.
6. Stop the nodes created in step 2.
7. Run git checkout handle-private-channel-hop-hints to checkout the code of this PR.
8. Run (cd migrate; cargo run -- --path ../tests/nodes/1/fiber/store) to start migration.
9. Run cargo build && (clear; cd ./tests/nodes/; ../../target/debug/fnn -d 1) to start node 1.
10. Run ldb --db=tests/nodes/1/fiber/store --secondary_path=/tmp/test/ dump --hex | awk '/0xC0/ {print $1}' | sed 's/0xC0/0x/g' | xargs -I __ curl -sS --json '{"id": "42", "jsonrpc": "2.0", "method": "get_payment", "params": [{"payment_hash": "__"}]}' again to check the payment session data have been migrated (by eyes).