[Backport] Remove forced setting of cache_lifetime to false in constructor and set default cache_lifetime to 3600

[mageprince]

Original Pull Request

#13762

As noted in issue #13595 the Magento\Theme\Block\Html\Footer block is not saved to cache. This issue has been looked at as part of #MLAU18

Description

In investigating the issue it was found that the footer block does not have a cache lifetime set and it also has code in its constructor to set the cache lifetime to false. This pull request removes the forcing of cache lifetime to false and sets the default value to 3600 as done so in the \Magento\Theme\Block\Html\Topmenu block.

Fixed Issues (if relevant)

1. loadCache for Block Magento\Theme\Block\Html\Footer dont work #13595

Manual testing scenarios

1. Disable full page caching so that block level caching may be observed
2. View a page that contains the footer block. E.g. homepage
3. Debug \Magento\Framework\View\Element\AbstractBlock::_saveCache on the first time a given footer block is loaded, and see that is is successfully saved to cache.
4. Debug \Magento\Framework\View\Element\AbstractBlock::_loadCache on a following request and confirm that the observed footer block is loaded from cache.

Contribution checklist

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All new or changed code is covered with unit/integration tests (if applicable)
• All automated tests passed successfully (all builds on Travis CI are green)

[magento-engcom-team]

Hi @mageprince. Thank you for your contribution.
We will aim to release these changes as part of 2.1.15.
Please check the release notes for final confirmation.