[Docs] add multiSearchXYZ functions

[Blargian]

Closes #1985 as part of the project to document missing or incomplete functions (1833), and standardize the formatting of functions. This PR makes changes to the multiSearchXYZ functions to align them to the standard format specified in 1833.

Changelog category (leave one):

• Documentation (changelog entry is not required)

Documentation entry for user-facing changes

• Documentation is written (mandatory for new features)
• multiSearchAllPositionsCaseInsensitive
• multiSearchAllPositionsCaseInsensitiveUTF8
• multiSearchAllPositionsUTF8
• multiSearchAnyCaseInsensitive
• multiSearchAnyCaseInsensitiveUTF8
• multiSearchAnyUTF8
• multiSearchFirstIndexCaseInsensitive
• multiSearchFirstIndexCaseInsensitiveUTF8
• multiSearchFirstIndexUTF8
• multiSearchFirstPositionCaseInsensitive
• multiSearchFirstPositionCaseInsensitiveUTF8
• multiSearchFirstPositionUTF8

[clickhouse-ci]

This is an automatic comment. The PR descriptions does not match the template.

Please, edit it accordingly.

The error is: More than one changelog category specified: 'Documentation (changelog entry is not required)', '[X] multiSearchAllPositionsCaseInsensitive'

[robot-ch-test-poll2]

This is an automated comment for commit 2c41bcb with description of existing statuses. It's updated for the latest CI running

✅ Click here to open a full report in a separate page

Successful checks

Check name	Description	Status
CI running	A meta-check that indicates the running CI. Normally, it's in success or pending state. The failed status indicates some problems with the PR	✅ success
Docs check	Builds and tests the documentation	✅ success
Mergeable Check	Checks if all other necessary checks are successful	✅ success
PR Check	There's no description for the check yet, please add it to tests/ci/ci_config.py:CHECK_DESCRIPTIONS	✅ success
Style check	Runs a set of checks to keep the code style clean. If some of tests failed, see the related log from the report	✅ success