Create sections for Learning about APIs, Administrating APIs, and Using the Caching Service in API ML Using section

[janan07]

Describe your pull request here: This PR addresses the reshuffling and minor refactoring of files into newly proposed sections in the API ML Using section and corresponds to Issue #3269.

List the file(s) included in this PR: api-mediaiton-caching-service, api-mediation-static-api-refresh, api-mediation-swagger-code-snippets, api-mediation-swagger-try-it-out, obtaining-information-about-api-services, onboard-wizard, sidebars.js

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[github-actions]

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[github-actions]

📁 The PR description is missing the file name(s) for the updated content. List all the files included in this PR so this information displays in our Zowe Docs GitHub Slack channel.

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[github-actions]

📁 The PR description is missing the file name(s) for the updated content. List all the files included in this PR so this information displays in our Zowe Docs GitHub Slack channel.

If you have addressed this issue already, refresh this page in your browser to remove this comment.

[github-actions]

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