feat!: drop node 10 support

[ddelgrosso1]

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Fixes #<issue_number_goes_here> 🦕

[generated-files-bot]

Warning: This pull request is touching the following templated files:

• .kokoro/continuous/node10/common.cfg - .kokoro files are templated and should be updated in synthtool
• .kokoro/continuous/node10/docs.cfg - .kokoro files are templated and should be updated in synthtool
• .kokoro/continuous/node10/test.cfg - .kokoro files are templated and should be updated in synthtool
• .kokoro/continuous/node8/common.cfg - .kokoro files are templated and should be updated in synthtool
• .kokoro/continuous/node8/test.cfg - .kokoro files are templated and should be updated in synthtool
• .kokoro/presubmit/node10/common.cfg - .kokoro files are templated and should be updated in synthtool
• .kokoro/presubmit/node10/docs.cfg - .kokoro files are templated and should be updated in synthtool
• .kokoro/presubmit/node10/lint.cfg - .kokoro files are templated and should be updated in synthtool
• .kokoro/presubmit/node10/test.cfg - .kokoro files are templated and should be updated in synthtool
• .kokoro/presubmit/node8/common.cfg - .kokoro files are templated and should be updated in synthtool
• .kokoro/presubmit/node8/test.cfg - .kokoro files are templated and should be updated in synthtool
• .github/workflows/ci.yaml - .github/workflows/ci.yaml (GitHub Actions) should be updated in synthtool