MySQL: Force-set prefer_column_name_to_alias in handler and set mysql_map_(fixed)_string_to_text_in_show_columns by default

[rschu1ze]

Some BI tools which connect to ClickHouse's MySQL port, run queries that succeed only with

• the analyzer enabled, or
• without analyzer and setting prefer_column_name_to_alias = 1.

Since prefer_column_name_to_alias is too impactful to enable it globally, it is now force-enabled for MySQL connections as a workaround. When the analyzer is the new default, this PR can be reverted.

This PR also enables settings mysql_map_string_to_text_in_show_columns and mysql_map_fixed_string_to_text_in_show_columns by default (which they should have been from the start already). This means that SHOW COLUMNS when called through the MySQL port now returns the expected MySQL-equivalent data types w/o further messing with configuration.

@slvrtrn

Changelog category (leave one):

• Improvement

Changelog entry (a user-readable short description of the changes that goes to CHANGELOG.md):

Connections through the MySQL port now automatically run with setting prefer_column_name_to_alias = 1 to support QuickSight out-of-the-box. Also, settings mysql_map_string_to_text_in_show_columns and mysql_map_fixed_string_to_text_in_show_columns are now enabled by default, affecting also only MySQL connections. This increases compatibility with more BI tools.

[clickhouse-ci]

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[clickhouse-ci]

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Please, edit it accordingly.

The error is: Changelog entry required for category 'Bug Fix (user-visible misbehavior in an official stable release)'

[robot-clickhouse-ci-1]

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