[GOBBLIN-701] Added the concept of secure job templates and job resolution callbacks.

[ibuenros]

Dear Gobblin maintainers,

Please accept this PR. I understand that it will not be reviewed until I have checked off all the steps below!

JIRA

• [ ] My PR addresses the following Gobblin JIRA issues and references them in the PR title. For example, "[GOBBLIN-XXX] My Gobblin PR"
  • https://issues.apache.org/jira/browse/GOBBLIN-XXX

Description

• [ ] Here are some details about my PR, including screenshots (if applicable):

Tests

• [ ] My PR adds the following unit tests OR does not need testing for this extremely good reason:

Commits

• [ ] My commits all reference JIRA issues in their subject lines, and I have squashed multiple commits if they address the same issue. In addition, my commits follow the guidelines from "How to write a good git commit message":
  1. Subject is separated from body by a blank line
  2. Subject is limited to 50 characters
  3. Subject does not end with a period
  4. Subject uses the imperative mood ("add", not "adding")
  5. Body wraps at 72 characters
  6. Body explains "what" and "why", not "how"

[ibuenros]

@sv2000 can you take a look when you get a chance?

[sv2000]

@ibuenros - I took a quick look at this PR. Looks good to me in general. Will add comments tomorrow. Looks like there are no conflicts with the base branch - so should be mergeable.