feat(dropdown): filtering and multi select improvements in dropdown

[ckrook]

Describe pull-request

We previosly had an issue with the dropdown component when filter:true & multiselect:true. To address this issue I clear the input when its focused. This makes better UX since the user can search on whatever they want. When the user blur the input they can see which selections have been done.

Issue Linking:

Choose one of the following options

• Jira: Add ticket number after CDEP-2758: CDEP-
• GitHub: Issue 738

How to test

Provide detailed steps for testing, including any necessary setup.

1. Go to Storybook,
2. Navigate to dropdown component
3. In the storybook controls, choose filter: true & multiselect true

Checklist before submission

• [x] I have added unit tests for my changes (if applicable)
• [x] All existing tests pass
• [x] I have updated the documentation (if applicable)

Suggested test steps

• [x] Browser testing (Chrome, Safari, Firefox)
• [x] Keyboard operability