feat(coderd/database/dbtestutil): set default database timezone to non-UTC in unit tests (#9672)

- Adds dbtestutil.WithTimezone(tz) to allow setting the timezone for a test database.
- Modifies our test database setup code to pick a consistently weird timezone for the database.
- Adds the facility randtz.Name() to pick a random timezone which is consistent across subtests (via sync.Once).
- Adds a linter rule to warn against setting the test database timezone to UTC.

cli/clitest/golden.go

@@ -26,7 +26,7 @@ import (
 // make update-golden-files
 var UpdateGoldenFiles = flag.Bool("update", false, "update .golden files")
 
-var timestampRegex = regexp.MustCompile(`(?i)\d{4}-\d{2}-\d{2}T\d{2}:\d{2}:\d{2}(.\d+)?Z`)
+var timestampRegex = regexp.MustCompile(`(?i)\d{4}-\d{2}-\d{2}T\d{2}:\d{2}:\d{2}(.\d+)?(Z|[+-]\d+:\d+)`)
 
 type CommandHelpCase struct {
 	Name string