Update Sample to allow sub-sampling and bulked samples

Use Cases

1. Take a sub-sample from another sample. This can occur in several cases, for example extracting DNA from a plant leaf tissue or making an aliquot of the sample.
2. Combining two or more samples into one bulked sample, for example for bulked analysis.

Proposed model changes

• Add the property sourceSamples to the Sample entity. The new property would have array of SampleMixture.
• A SampleMixture has the properties sampleDbId which will be the sampleDbId of the source sample and mixturePercentage which has type number, and is the relative contribution of the source sample to this sample.

Implementation by use case

1. The sub-sample would have a single element in the sourceSamples property, which have a mixturePercentage of 100.0 and the sampleDbId of the sample from which this sub-sample was taken. The germplasm of the sub-sample will be the same as the source sample.
2. The bulked sample would have two more elements in the sourceSampleDbIds property, which will have as mixturePercentages the relative contribution of the source sample to this sample and sampleDbId of the samples which were using the bulk. If the source samples are all from the same germplasm then this will be germplasm of the sample. If the germplasm are different, then the germplasm of this sample would need to be a new germplasm formed by the combination of all the district germplasm though a maintenance breeding method.

[ggeurts]

Wouldn't a subsample just have the source sample as observation unit?