Implementation of Feature Request #2802

[justinzhu17]

This is me and my partner's attempt to implement feature request plotly#2802

Start with a description of this PR. Then edit the list below to the items that make sense for your PR scope, and check off the boxes as you go!

Contributor Checklist

• [ ✔️] I have broken down my PR scope into the following TODO tasks
  • [✔️ ] Create a new function call that deletes the data in a heatmap
  • [ ✔️] Test to make sure all data is deleted and data format is not messed up.
• [✔️ ] I have run the tests locally and they passed. (refer to testing section in contributing)
• I have added tests, or extended existing tests, to cover any new features or bugs fixed in this PR

optionals

• I have added entry in the CHANGELOG.md
• If this PR needs a follow-up in dash docs, community thread, I have mentioned the relevant URLS as follows
  • this GitHub #PR number updates the dash docs
  • here is the show and tell thread in Plotly Dash community