Add support for setting check_interval

[fkleon]

Add support to set check_interval in the global config section.

check_interval: Defines the interval length, in seconds, between the runner checking for new jobs.
The default value is 3. If set to 0 or lower, the default value is used.

See https://docs.gitlab.com/runner/configuration/advanced-configuration.html#the-global-section

This defaults to 0 which matches the default auto-generated config, and simply causes GitLab runner to use its default value (see above). So this shouldn't cause any change in behaviour for existing users of this role.

[fkleon]

@guenhter just wondering if you can have another look at this?

[guenhter]

@fkleon Thx for this contribution

maybe you can keep your eyes open for incoming issues which might be caused by a this change.