Update EBNF for password options

[qiancai]

For reviewers: Preview ebnf on https://kennytm.github.io/website-docs/dist/

What is changed, added or deleted? (Required)

The PASSWORD REQUIRE CURRENT DEFAULT syntax is accepted to be able to parse the output of SHOW CREATE USER from MySQL. Especially as this is added by default by MySQL even if not specified when creating the user.

In MySQL PASSWORD REQUIRE CURRENT and PASSWORD REQUIRE CURRENT OPTIONAL are also accepted, but TiDB doesn't and the parser won't accept this.

As there is no password_require_current system variable in TiDB and no other options are accepted this syntax is meaningless / ignored.

See also: https://dev.mysql.com/doc/refman/8.4/en/password-management.html#password-reverification-policy

Note that the docs suggested that CREATE USER 'foo3'@'%' IDENTIFIED BY 'abc' DEFAULT ROLE 'myrole' should be accepted by TiDB with the role being ignored, but that doesn't seem to be the case.

Which TiDB version(s) do your changes apply to? (Required)

Tips for choosing the affected version(s):

By default, CHOOSE MASTER ONLY so your changes will be applied to the next TiDB major or minor releases. If your PR involves a product feature behavior change or a compatibility change, CHOOSE THE AFFECTED RELEASE BRANCH(ES) AND MASTER.

For details, see tips for choosing the affected versions.

• master (the latest development version)
• v8.2 (TiDB 8.2 versions)
• v8.1 (TiDB 8.1 versions)
• v8.0 (TiDB 8.0 versions)
• v7.6 (TiDB 7.6 versions)
• v7.5 (TiDB 7.5 versions)
• v7.1 (TiDB 7.1 versions)
• v6.5 (TiDB 6.5 versions)
• v6.1 (TiDB 6.1 versions)
• v5.4 (TiDB 5.4 versions)
• v5.3 (TiDB 5.3 versions)
• v5.2 (TiDB 5.2 versions)
• v5.1 (TiDB 5.1 versions)

What is the related PR or file link(s)?

• This PR is translated from: Update EBNF for password options docs#18090
• Other reference link(s):

pingcap/tidb#53306

Do your changes match any of the following descriptions?

• Delete files
• Change aliases
• Need modification after applied to another branch
• Might cause conflicts after applied to another branch

[ti-chi-bot]

@CbcWestwolf: adding LGTM is restricted to approvers and reviewers in OWNERS files.

In response to this:

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository.

[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2024-07-03 02:13:38.434942016 +0000 UTC m=+1376944.920430842: ☑️ agreed by hfxsd.

[qiancai]

/approve

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: qiancai

The full list of commands accepted by this bot can be found here.

The pull request process is described here

Needs approval from an approver in each of these files:

• OWNERS [qiancai]

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-8.2: #17850.