webhooks from non-master commits must be ignored

[yegor256]

Currently, we respond to all webhook-arrived commits. Instead, let's react only if the commit is in the default branch.

[pnatashap]

For Github request we can see default_branch and master_branch parameters (and ref for destination branch):
{ "ref": "refs/heads/master", ... "repository": { ... "default_branch": "master", "master_branch": "main", }, ... }
so we must select which one should be used.
May be also a new parameter can be introduced to config, which branch should be used: master, default, all (for backward capability if anybody needed)

For GitLab we can see only default_branch (https://docs.gitlab.com/ee/user/project/integrations/webhook_events.html#push-events)
{ ... "ref": "refs/heads/master", "project":{ ... "default_branch":"master", }, }

[pnatashap]

Looks like it is better to use master only, in case of merge conflicts with master will be problems in pull logic