Ability to ask CLOWarden to validate a PR manually

[tegioz]

At the moment, when a PR is created or synchronized (i.e. new commits are pushed), CLOWarden validates the configuration. Most of the time this is enough, but there are some cases in which it'd be handy to be able to trigger a validation job manually.

One example would be when trying to add a maintainer to a team who isn't a member of the organization yet. When this situation happens, CLOWarden will catch the problem and report it. But this problem needs to be fixed by adding that user to the organization manually, not making any changes to the configuration files. So CLOWarden won't trigger a new validation automatically.

In this situation, it might be handy to be able to type a command in a comment, something like /clowarden-validate (similar to how GitVote works), to double check everything is all right before proceeding with the PR merge. In the case of the example above, until this feature is ready, the PR will need to be merged once the user has been added to the organization, without a second validation.