Added users data to history table

[losgrandes]

Background

Idea behind this PR is to add information about DB users who executed a query to the history table. I've decided to add JSON column to store array of users for each query. There are probably more elegant solutions, but I wanted to keep "one table" concept.

Summary of changes

• added optional usernames JSON type column with support for it in history table
• updated documentation
• updated existing and added new tests case

[svetasmirnova]

Thank you for the contribution. You modified auto-generated code that will be rewritten after we run , ./utils/update-modules. Please add your changes into lib/QueryHistory.pm, then update modules in all tools as described in CONTRIBUTING.md

[svetasmirnova]

Please update lib/QueryHistory.pm

[losgrandes]

Thank you for the contribution. You modified auto-generated code that will be rewritten after we run , ./utils/update-modules. Please add your changes into lib/QueryHistory.pm, then update modules in all tools as described in CONTRIBUTING.md

My apologies for overlooking this.
I've run for t in bin/*; do ./util/update-modules ${t} QueryHistory; done and committed these changes. Should be good.
Thanks.

[svetasmirnova]

Changes look good for me, thank you!

But MySQL user accounts consist of two parts: usernames and hosts. E.g., sveta@percona.com is not the same user as sveta@my.blog. Maybe it makes sense to store host part too?

[svetasmirnova]

Please fix this stalled table name in the user manual part of the code too (query_review_history -> query_history).

[losgrandes]

Changes look good for me, thank you!

But MySQL user accounts consist of two parts: usernames and hosts. E.g., sveta@percona.com is not the same user as sveta@my.blog. Maybe it makes sense to store host part too?

This is very good idea, Sveta. In this code change I have reused already available user data which doesn't contain host information.
Adding that info requires reworking tools' core logic, which I would like to avoid currently.
I think it would be safer to add it later. WDYT?

[svetasmirnova]

Host is defined as part of $ea->results->{'classes'}{$item}, so I do not think it will require rewriting the tool's core logic. I suggest adding it now, together with the new "user" column.

Please also fix formatting: Percona Toolkit uses 3 spaces for indentation.