Update README to document max_upload_retries and max_copy_retries configuration options

- Added descriptions for the max_upload_retries and max_copy_retries configuration options in the README.
- max_upload_retries: Specifies the maximum number of retries for file uploads to Snowflake. Default value is 3.
- max_copy_retries: Specifies the maximum number of retries for COPY operations in Snowflake. Default value is 3. Retries are triggered for transient errors such as communication failures.
- Improved documentation to help users understand the retry configurations and their default behaviors.

Author: kentoyoshida

README.md

@@ -23,6 +23,8 @@ Snowflake output plugin for Embulk loads records to Snowflake.
 - **retry_limit**: max retry count for database operations (integer, default: 12). When intermediate table to create already created by another process, this plugin will retry with another table name to avoid collision.
 - **retry_wait**: initial retry wait time in milliseconds (integer, default: 1000 (1 second))
 - **max_retry_wait**: upper limit of retry wait, which will be doubled at every retry (integer, default: 1800000 (30 minutes))
+- **max_upload_retries**: maximum number of retries for file upload to Snowflake (integer, default: 3).
+- **max_copy_retries**: maximum number of retries for COPY operations in Snowflake (integer, default: 3). Retries occur when transient errors such as communication failures happen during the COPY process.
 - **mode**: "insert", "insert_direct", "truncate_insert", "replace" or "merge". See below. (string, required)
 - **merge_keys**: key column names for merging records in merge mode (string array, required in merge mode if table doesn't have primary key)
 - **merge_rule**: list of column assignments for updating existing records used in merge mode, for example `"foo" = T."foo" + S."foo"` (`T` means target table and `S` means source table). (string array, default: always overwrites with new values)