Add doneButton assistive text property to Filter

[andrycf]

Add dynamic label Button popover for Filter

Fixes #

Additional description

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CONTRIBUTOR checklist (do not remove)

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• [ ] Mocha, Jest (Storyshots), and components/component-docs.json CI tests pass (npm test).
• [ ] Tests have been added for new props to prevent regressions in the future. See readme.
• [ ] Review the appropriate Storybook stories. Open http://localhost:9001/.
• [ ] Review tests are passing in the browser. Open http://localhost:8001/.
• [ ] Review markup conforms to SLDS by looking at DOM snapshot strings.

REVIEWER checklist (do not remove)

• [ ] CircleCI tests pass. This includes linting, Mocha, Jest, Storyshots, and components/component-docs.json tests.
• [ ] Tests have been added for new props to prevent regressions in the future. See readme.
• [ ] Review the appropriate Storybook stories. Open http://localhost:9001/.
• [ ] The Accessibility panel of each Storybook story has 0 violations (aXe). Open http://localhost:9001/.
• [ ] Review tests are passing in the browser. Open http://localhost:8001/.
• [ ] Review markup conforms to SLDS by looking at DOM snapshot strings.

  Required only if there are markup / UX changes

• [ ] Add year-first date and commit SHA to last-slds-markup-review in package.json and push.
• [ ] Request a review of the deployed Heroku app by the Salesforce UX Accessibility Team.
• [ ] Add year-first review date, and commit SHA, last-accessibility-review, to package.json and push.
• [ ] While the contributor's branch is checked out, run npm run local-update within locally cloned site repo to confirm the site will function correctly at the next release.

[welcome[bot]]

Thanks for opening this pull request! :100:

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[salesforce-cla[bot]]

Thanks for the contribution! Before we can merge this, we need @andrycf to sign the Salesforce.com Contributor License Agreement.

[interactivellama]

Great catch! Please sign the CLA and ensure tests pass. It looks like linting here.