In this commit, the `MigrateGraphToSQL` function is expanded to migrate
the channel and channe policy data. Both of these have the special case
where the kvdb store records may contain invalid TLV. If we encounter a
channel with invalid TLV, we skip it and its policies. If we encounter a
policy with invalid TLV, we skip it.
The `TestMigrateGraphToSQL` and `TestMigrationWithChannelDB` tests are
updated accordingly.
This commit expands MigrateGraphToSQL so that it migrates all the graph
nodes from kvdb to SQL.
The TestMigrateGraphToSQL test is updated to cover the basic
LightningNode cases. A new test, `TestSQLMigrationEdgeCases`, is also
added and a case is added to tests the edge case where a node exists in
our kvdb store that has invalid TLV bytes.
In this commit, the basic framework for the graph SQL migration is
added. This sets us up for the commits to follow which will add
migration logic for each table in the graph commit by commit.
