MDEV-36297: Ability to backup selected partitions only

[slawomir-pryczek]

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Description

This code adds ability to backup selected partition(s) by mariadb-dump by using --partition-separator=@ and then specifying partition name in table's name, eg. mytable1@p0,p1. There should be no side effects, support for selecting partition(s) is disabled by default. ./mariadb-dump -umyuser -pmypass -h127.0.0.1 mydatabase _test1@p0,p1 _test2@p0 --partition-separator=@

Release Notes

Ability to backup specific partitions with mariadb-dump by using --partition-separator and specifying partition list in table's name

How can this PR be tested?

Won't affect mariadb-server, will try to write test case if that gets accepted.

Basing the PR against the correct MariaDB version

• [X] This is a new feature or a refactoring, and the PR is based against the main branch.
• [ ] This is a bug fix, and the PR is based against the earliest maintained branch in which the bug can be reproduced.

PR quality check

• [x] I checked the CODING_STANDARDS.md file and my PR conforms to this where appropriate.
• [X] For any trivial modifications to the PR, I am ok with the reviewer making the changes themselves.