Added checkbox to load script in an asynchronous way

[paragthakurtcs]

• Please add check box for “async” attribute in to the “Tag Manager Tool Container Path” section.
• Check box should appear at the bottom of the “Tag Manager Tool Container Path” section, and should be accompanied by texts “load asynchronously (recommended)”.
• Check box should be checked by the default, and if checked, then the upon the deployment the attribute “async” should be added to the above development and production paths.
• Please verify that the paths values within “Footer Code” section are not mandated. Right below “Footer Code” section title please add text “not required for asynchronous load”.

REF JIRA - https://digitalpfizer.atlassian.net/browse/US-1425