Create OEM provider and provider snap (New)

[sampaio23]

Description

This commit creates the checkbox-oem provider and adds the necessary files to be able to pack it as a snap. This uses the new Custom Frontend Interface available on checkbox.

Resolved issues

Resolves: https://warthogs.atlassian.net/browse/OEIOT-695

Documentation

Tests

Follow contrib/checkbox-oem/README.md to test.

[EthanHsieh]

Hi @sampaio23,
As discussed, please create a separate snap for classic images. For UC24 and classic 24.04, let's follow the existing design in project providers rather than using a custom frontend.

[Hook25]

Hello, I strongly disagree with keeping around the blobs of bash and prayers that were the old classic providers. We are moving away from them because they introduce a whole category of issues and it is unclear to me what benefits they bring. Why do you want to use the old design?

[EthanHsieh]

Hi @Hook25
We also aim to adopt the custom frontend wherever possible. The reason we have not fully adopted the custom frontend is that some existing projects are still using the previous design. After discussing with the QA team, we decided to start introducing it in UC26. As for classic 26.04, there are still some issues to be resolved, and the QA team will follow up.

[sampaio23]

Hi @EthanHsieh ,
I've updated the PR with the existing design. Please help to review.
Thanks!