Export a station's OCPP message log as NDJSON

The same messages and filters as the log, oldest first, one JSON object per line (application/x-ndjson), at most 10,000 lines. When more remain, or the charging core fails mid-export, a last line without an id carries next_cursor (and error): pass it as cursor with the same filters to continue. since and until are ISO 8601; until defaults to now and since to 24 hours before until, and one request covers at most 7 days (422 time_range_invalid). action (repeatable, up to 20) keeps only those OCPP actions; a reply carries its request's action. Payloads are redacted before they leave the API: passwords, keys and secret configuration values read [redacted], HTTP Basic and URL credentials and query strings are masked, ID tokens show their last 4 characters, and certificates are cut to 32 characters. Requires stations:diagnostics, which team owners, admins and developers and Ivora support hold, and operators, viewers and billing members never do.