Add logger submodule

Closes #3475570

This MR creates a new module search_api_logger with the following functionality:

1. Expose TypedData plugin LogEntry, accompanied by LogEntryDataDefinition. Fields in LogEntryDataDefinition match those of dblog_schema()
2. Expose Plugin/search_api/datasource/Log plugin that represent log entry.
3. Expose LoggerInterface implementation SearchApiLog.

Then go parts that I'm not sure about:

1. SearchApiLog pushes all log entries to search_api index with predefined name "logs". If such index does not exist or is disabled, SearchApiLog::log() does nothing.
2. There are predefined configurations for search_api.index.logs and accompanying view views.view.logs in config/install