Galera feature: Retry applying writesets at slaves

[plampio]

A new Galera feature that allows retrying of applying of writesets at slave nodes (codership/mysql-wsrep-bugs/#1619). Currently replication applying stops for first non ignored failure occurring in event applying, and node will do emergency abort (or start inconsistency voting). Some failures, however, can be concurrency related, and applying may succeed if the operation is tried at later time.

This feature introduces a new dynamic global option variable "wsrep_applier_retry_count" that controls the retry-applying feature: a zero value disables retrying and a positive value sets the maximum number of retry attempts. The default value for this option is zero, which means that this feature is disabled by default.

• The Jira issue number for this PR is: MDEV-______

Description

TODO: fill description here

Release Notes

TODO: What should the release notes say about this change?
Include any changed system variables, status variables or behaviour. Optionally list any https://mariadb.com/kb/ pages that need changing.

How can this PR be tested?

TODO: modify the automated test suite to verify that the PR causes MariaDB to behave as intended.
Consult the documentation on "Writing good test cases".

If the changes are not amenable to automated testing, please explain why not and carefully describe how to test manually.

Basing the PR against the correct MariaDB version

• 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

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

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