[WIP] go.mod: update all dependencies

[kennytm]

What problem does this PR solve?

Update the dependencies

What is changed and how it works?

• PingCAP dependencies (pd, tidb-tools) are updated to v3.0.0.
• The other dependencies are updated to the latest release version, or master if no release is defined.

Code changes involved:

• prometheus.Handler has been moved into a subpackage promhttp.
• Add completely new push syntax prometheus/client_golang#381 replaced the push.AddFromGatherer API
• Remove strict mode go-sql-driver/mysql#676 removed strict mode and MySQLWarnings

Check List

Tests

• Unit test

Code changes

Side effects

Related changes

[Deardrops]

go-sql-driver/mysql has remove support of strict mode.
Is there any mysql driver can enable strict mode and MySQLWarnings?

[kennytm]

@Deardrops The wiki says you should enable strict mode via sql_mode instead.

[Deardrops]

@Deardrops The wiki says you should enable strict mode via sql_mode instead.

@kennytm thanks