CI: fail PR if it does not have required labels

[shlomi-noach]

Description

Fixes #8146

Adding a ci job to fail a PR if it does not have at least one Component: ... label and at least one Type: ... label.

Related Issue(s)

• Add CI job to validate PR labels #8146

Checklist

• Tests were added or are not required
• Documentation was added or is not required

Deployment Notes

[shlomi-noach]

Right now this PR fails because it does not have a Type: ... label: https://github.com/vitessio/vitess/runs/2617745882?check_suite_focus=true

So i'll now add a Type: ... label and see if CI passes. Note: I will have to trigger the CI manually because the workflow file does not exist in the default branch (master) because that's how it works; when the PR is merged, then CI gets retriggered upon any label change, automatically.

[shlomi-noach]

yay, as expected, CI passes: https://github.com/vitessio/vitess/runs/2617806212?check_suite_focus=true

[systay]

❤️