Wdfn 768 - Convert the legend component to vue

Before making a pull request

• Put the appropriate EXEMPT flag if needed in the MR title (see https://practices.wma.chs.usgs.gov/practice/peer_code_review/)
• Run all linters (make lint)
• Run all tests (make test)
• Update the changelog appropriately
• If making a release, update code.json metadataLastUpdated and bump CHANGELOG.md to next version.

Description

Added a vue component for the hydrograph legend. Added the graph controls component to the hydrograph app.

After making a pull request

• If appropriate, put the link to the PR in the JIRA ticket
• Assign someone to review unless the change is trivial