Update ephemeral builder metadata

[scottfrederick]

To maintain parity with pack, metadata for the ephemeral builder container should:

• Include a structure in the container metadata field Config.Labels["io.buildpacks.builder.metadata"] that identifies Spring Boot as the creator along with the Boot version:

"createdBy" : {
  "name" : "Spring Boot",
  "version" : "2.3.0.BUILD-SNAPSHOT"
}

• Set the container creation date to 1980-01-01T00:00:01Z (Windows epoch + 1 second)

[snicoll]

@scottfrederick I built an image this morning with the latest snapshot and this is what docker images shows for it:

snicoll78/demo-image                            latest                       24e14746abe3        40 years ago 

I don't know where the miss-date is coming from but I think this is something we should be looking at.