Support for Gradle Configuration Cache

**Environment**:

- *Jib version:* 2.8.0
- *Build tool:* Gradle 6.8.1
- *OS:* Mac

**Description of the issue**:

Gradle 6.8 has a new configuration cache feature that helps to improve build performance. Unfortunately, there are some restrictions on what plugins can use and jib is currently not compatible with this. I don´t think that jib, in particular, is bad wrt to build performance, still, I think it would be cool if it supports the configuration cache at some point :)

**Steps to reproduce**:
1. `gradle --configuration-cache jib`

**Log output**:
```
- Task `:html5-controller:jib` of type `com.google.cloud.tools.jib.gradle.BuildImageTask`: cannot serialize object of type 'org.gradle.api.internal.project.DefaultProject', a subtype of 'org.gradle.api.Project', as these are not supported with the configuration cache.
See https://docs.gradle.org/6.8.1/userguide/configuration_cache.html#config_cache:requirements:disallowed_types
- Task `:html5-controller:jib` of type `com.google.cloud.tools.jib.gradle.BuildImageTask`: invocation of 'Task.project' at execution time is unsupported.
See https://docs.gradle.org/6.8.1/userguide/configuration_cache.html#config_cache:requirements:use_project_during_execution
```