Combine Status filter and Type filter into a single filter

[SAN-MUYUN]

Summary:

Fixes CATcher-org#402

Type of change:

• ✨ New Feature/ Enhancement
• 🧪 Tests Update

Changes Made:

Combine the Type and Status filter into a single filter. Delete functions that are implemented to support the interactions between the two filters, which are no longer needed.

Milestone filter will now display both "Issues without a milestone" and "PRs without a milestone" options at all times, which matches the behavior when the "All" option is selected under the original "Type" filter.

Write basic test cases for applyDropdownFilter function.

Screenshots:

Before:

After:

Proposed Commit Message:

Combine Type filter and Status filter into a single filter

Combining the filters provide a more straight forward UI that is simpler for users to
navigate and filters the Issues and PRs.

Checklist:

• I have tested my changes thoroughly.
• I have created tests for any new code files created in this PR or provided a link to a issue/PR that addresses this.
• I have added or modified code comments to improve code readability where necessary.
• I have updated the project's documentation as necessary.