Update JTBD to align with terms used in the JTBD playbook

Why is this change being made?

Background

While updating the documentation for UX themes to correspond with JTBD, I found some inconsistencies in our JTBD documentation that present challenges to both processes' success.

1. Our JTBD documentation differs in the terminology used by industry leaders, Kalback JTBD Playbook, Intercom, etc. Though seemingly inconsequential, this differentiation leads to confusion and low adoption of the JTBD process. A good example of this is using job statement instead of job story, so we don't confuse them with user stories. Job statements themselves are significantly different from Job stories and play a pivotal role in formulating the JTBD. A job statement is the job itself structured in a programmatic way, and without this foundation, the creation of JTBD will continue to be met with confusion.
2. Rephrased sub-job to small job following Kalbach and Intercom's terminology.
3. Rephrased task to micro-job following Kalbach and Intercom's terminology.
4. Added more concrete examples.
5. Added a diagram detailing how the Main job, small jobs, and micro-jobs relate.

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