Gateway: add runtime job entry to serverless job object

[IceKhan13]

What is the expected enhancement?

1. Add runtime jobs id entry to serverless job entry, so that they can be associated to each other.

2. Add runtime jobs ids to rest api

Epic #1162

[akihikokuroda]

Does this closed PR #977 works as the base of this issue? If so, I can revise and rebase it.

[psschwei]

I think it does

[IceKhan13]

I think it does too :)

One comment though, probably we want separate entity model for that in PR, not text field.

Something like

class Job(models.Model):
   ...

class RuntimeJob(models.Model):
   job = models.ForeignField(Job, ...)