Enables numeric values for FQDN in workspace:agent

What does this MR do and why?

Enables numeric values for FQDN in workspace:agent

Specifically for the unqualified host label.

Unqualified hostname part of a domain is the part before the first dot. By default validates_hostname gem does not allow this label to be numeric. This is enabled because this is a completely valid part of a domain.

Changelog: fixed EE: true

References

• https://github.com/KimNorgaard/validates_hostname/blob/v1.0.13/lib/validates_hostname.rb#L210

• In case of numeric unqualified host label the agent config is not be saved and this error is be logged.

  => #<ActiveModel::Errors [#<ActiveModel::Error attribute=dns_zone, type=unqualified hostname part cannot consist of numeric values only, options={}>]>

How to set up and validate locally

• Try to save an agent config with a numeric qualified host label, for example, 1.domain.com
• The agent config should be saved.

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