chore: add renovate rule so logback do not bump major versions.

[zhumin8]

setting up this so logback versions 1.3.x used to test slf4j 1.x won't be updated. side effect is 1.5.x won't get updates either when 1.6.x comes out.

[zhumin8]

@JoeWang1127 Do you think this makes sense while we figure out a better way to only disable for 1.2.x? So we don't get upgrades like https://github.com/googleapis/sdk-platform-java/pull/3704

[sonarqubecloud[bot]]

Quality Gate passed for 'gapic-generator-java-root'

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[sonarqubecloud[bot]]

Quality Gate passed for 'java_showcase_integration_tests'

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud