Support running an SQL file on init (1.3)

[staticlibs]

This is a backport of the PR #252 to v1.3-ossivalis stable branch.

This change adds support for session_init_sql_file connection option, that allows to speficy the path to an SQL file in local file system, that will be read by the driver and executed in a newly created connection before passing it to user.

By default the file is initalized only once per database, on the first connection established to this DB.

For :memory: connection-private DBs it effectively executed once per connection.

In addition to the DB init, it supports executing a part of the SQL file for every connection. It looks for the specific marker:

/* DUCKDB_CONNECTION_INIT_BELOW_MARKER */

in the SQL file. If this marker is present - everything before the marker is executed on DB init, and everything after this marker - on connection init.

DB init is not re-run when the DB is closed and re-opened after the last connection to it was closed and then new one created. If such re-init is necessary - jdbc_pin_db option is supposed to be used instead.

It is understood, that this feature can be security sensitive (it effectively implements an RCE entry) in contexts, where other applications/processes/users can control the appending to user-specified connection string or re-writing the specified file in local file system. The following security measures are taken to mitigate that:

• session_init_sql_file option can only be specified in the connection string itself, it is not accepted as part of connection Properties
• session_init_sql_file option must be specified as the first option in the connection string, for example: 'jdbc:duckdb:;session_init_sql_file=/path/to/init.sql'
• session_init_sql_file_sha256=<sha56sum_of_sql_file> option can be specified, the file contents SHA-256 sum is checked againts this value
• session_init_sql_file_sha256 option can only be specified in the connection string itself
• session_init_sql_file and session_init_sql_file_sha256 options cannot be specified multiple times
• content of the SQL file are available to the running code using DuckDBConnection#getSessionInitSQL() method

Testing: new tests added in a separate file.