### Summary

When adding content to a file using `blockinfile`, it is hard to prepend/append a blank line to the block.

e.g. this would be the result when using EOF:
````ini
# network settings
foo = bar
baz = qux
# BEGIN ANSIBLE MANAGED BLOCK
something = 123
# END ANSIBLE MANAGED BLOCK
````

That's hard to use. This would be better (and conventional):
````ini
# network settings
foo = bar
baz = qux

# BEGIN ANSIBLE MANAGED BLOCK
something = 123
# END ANSIBLE MANAGED BLOCK
````

That blank space is so important. Without it the file becomes unreadable, especially when there are multiple blocks, or the blocks are interspersed throughout the file (not BOF or EOF).

There are many related questions on SO about this. For example, [here's one with 12k views](https://stackoverflow.com/q/64687350/9971404).

The only way to do this idempotently is to use two tasks, one for the blank line and one for the block. And it's nasty.

Please consider adding a new option to `blockinfile` to allow prepending/appending blank lines?

### Issue Type

Feature Idea

### Component Name

blockinfile

### Additional Information

<!--- Paste example playbooks or commands between quotes below -->
```yaml (paste below)

```


### Code of Conduct

- [X] I agree to follow the Ansible Code of Conduct
marker_end:
    required: false
    description:
    - This will be inserted at C({mark}) in the closing ansible block O(marker).
    type: str
    default: END
    version_added: '2.5'
notes:
  - When using 'with_*' loops be aware that if you do not set a unique mark the block will be overwritten on each iteration.
  - As of Ansible 2.3, the O(dest) option has been changed to O(path) as default, but O(dest) still works as well.
  - Option O(ignore:follow) has been removed in Ansible 2.5, because this module modifies the contents of the file
    so O(ignore:follow=no) does not make sense.
  - When more then one block should be handled in one file you must change the O(marker) per task.
extends_documentation_fragment:
    - action_common_attributes
    - action_common_attributes.files
    - files
    - validate
attributes:
    check_mode:
        support: full
    diff_mode:
        support: full
    safe_file_operations:
      support: full
    platform:
      support: full
      platforms: posix
    vault:
      support: none