Add templates for evaluation board user guides

[IuliaCMoldovan]

• Added the initial template
• Added an example with AD9081
  • Quick start for A10SoC, VCK190 and ZCU102
• Restructured the ADRV9026 example by the new template. Renamed the folder to ADRV902X because the same evaluation board is used for ADRV9029 as well
• Added corresponding images
• Moved the whole eval/user-guide folder to solutions/reference-designs, each project in its folder. No more sections like "transceivers" or "adc"

Type

• Documentation
• Bug fix
• New feature
• Continuous integration

Checklist

• I have performed a self-review of changes
• I have followed the guidelines:
  • https://analogdevicesinc.github.io/documentation/contributing/docs_guidelines.html
  • https://analogdevicesinc.github.io/doctools/docs_guidelines/index.html
  • https://analogdevicesinc.github.io/documentation/contributing/creating_new_pages.html#documentation-structure
• I have used the appropriate roles and directives:
  • https://analogdevicesinc.github.io/doctools/docs_guidelines/roles.html
  • https://analogdevicesinc.github.io/doctools/docs_guidelines/directives.html
• I ensured that binary data was committed to git lfs:
  • https://analogdevicesinc.github.io/documentation/contributing/creating_new_pages.html#adding-images-and-other-binary-files
• I have built the pages I edited or created, using either make html or adoc serve:
  • https://analogdevicesinc.github.io/doctools/cli.html#serve
• I have signed-off my commits and believe my contribution improves the repository.