[CHECKBOX-1447] Github workflow for promoting beta to candidate (Infra)

[boukeas]

Description

This PR introduces a workflow for promoting Checkbox beta to candidate, meeting the requirements in CHECKBOX-1447.

Specifically, it is able to launch multiple runs on different queues, for different Checkbox snap runtimes/tracks, as well as .deb packages. For each run, the main part of the workflow creates and submits a Testflinger job that is able, among others, to retrieve a manifest for the particular device it is running on and run the canary test plan.

The workflow makes use of the scriptlets and tools in the hwcert-jenkins-tools repo.

Points to note

• The PR introduces a template for the job file that will be submitted to Testflinger. The workflow instantiates the template using specific environment variables before submitting the job to Testflinger. This approach separates the Github workflow from the submitted job. Indeed, the job file can be instantiated, submitted and tested independently of the Github workflow, using just the Testflinger CLI.
• Two resource files from the Checkbox repo are (currently) required by the job. These files are retrieved from the repo, which is checked out in one step of the workflow, and provided as attachments to the job, so that they are available on the agent when the job script, i.e. the test_cmds, are executed. This is a completely new approach: so far, the only way for files to find their way on to the agent was (a) to provide their contents inline, i.e. as here docs within the test_cmds or (b) to retrieve them from a public repository, after cloning it.

Resolved issues

Resolves CHECKBOX-1447.

Tests

Example workflow runs for sample snap and debian package.

[Hook25]

+1, will follow this up on this pulse