Add appendTo features of go-datepicker module

[amitpatra91]

PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines
• Tests for the changes have been added
• Docs have been added or updated

PR Type

What kind of change does this PR introduce?

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• CI related changes
• Documentation content changes
• Style Update (CSS)
• Other... Please describe:

What is the current behavior?

After clicking on the calendar icon calendar body was hiding behind of modal body.

Resolves 717

What is the new behavior?

Now it's displayed on the modal body.

Does this PR introduce a breaking change?

• Yes
• No

[grahamhency]

This is a good first pass, I think we can make some improvements and simplifications though. Please see my comments.

Also, I looked at the deploy preview for this to see the functionality and there is a bug. To reproduce:

1. Go to the example in the docs and open the modal
2. Open the datepicker
3. Click the close icon for the modal
4. The datepicker remains on the page

Screenshot:

[grahamhency]

Sorry for the delay, had to do some research and some trial & error to figure out how to not use the setTimeout and other things. I've made some more comments, let me know your thoughts.

[grahamhency]

Just one more comment on types.

Additionally, I think we need to write some tests for these changes and also fix the broken tests.

[grahamhency]

Code is good, but there are broken tests and we need tests for the updated code.

[grahamhency]

The changes you proposed for the tests is not a solution. Those tests should still be in place an pass successfully.