Docs organize user setting profiles

[DanRoscigno]

This adds an overview to the settings section of the docs explaining the difference between global server settings and query-level settings and provides examples of the different ways of setting the query-level settings.

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Related to ClickHouse/clickhouse-docs#2299 , I will tackle that one next (it should be very similar)

[robot-ch-test-poll1]

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[rschu1ze]

This is the current order of doc pages:

In my view, a more logical order would be:

1. Settings Overview
2. Configuration files
3. User Settings
4. Settings Profiles
5. Constraints on Settings
6. Global Server Settings
7. Merge Tree Settings
8. Core Settings
9. Format Settings
10. Restrictions on Query Complexity

Pages "Permissions for Queries" and "Memory Overcommit" look out-of-place and are ideally integrated into an existing page. But that can also be done separately.

[rschu1ze]

There are two main groups of ClickHouse settings:

• Global server settings
• Session and query-level settings

[rschu1ze]

The main distinction between global server settings and session / query-level settings is that global server settings must be set in configuration files while session / query-level settings can be set in configuration files or with SQL queries.

[rschu1ze]

Let's rename this to include "session-level" settings.

[rschu1ze]

@DanRoscigno The auto-merger submitted this PR a bit too early into the codebase :-) Kindly see my remaining comments (they are not critical).