Batch up writes for monitor service

[jwilder]

The monitor service was writing one big batch for all stats. If this
batch was large, it causes some slower and more expensive write paths
to be taken that incur a lot of memory allocations. This changes the
monitor service to write in batches of up to 5000 points which should
avoid the slower paths.

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• CHANGELOG.md updated
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• InfluxQL Spec updated
• Provide example syntax
• Update man page when modifying a command
• Config changes: update sample config (etc/config.sample.toml), server NewDemoConfig method, and Diagnostics methods reporting config settings, if necessary
• InfluxData Documentation: issue filed or pull request submitted <link to issue or pull request>