MI - USE CASES section (Initial drafts and Navigation structure)

[nilminiwso2]

This issue is to get started on the 'Use Cases' section [1] of the Micro Integrator docs.

• Move all the related content (from the previous doc spaces) to github.
• Organize the content under 'Examples', 'Guides', and 'Tasks'. This content was previously dispersed across the doc space.
• Update the yaml with the navigation structure [2].

[1] https://github.com/wso2/docs-ei/tree/master/en/micro-integrator/docs/use-cases
[2] https://github.com/wso2/docs-ei/blob/master/en/micro-integrator/mkdocs.yml

[nilminiwso2]

Done.