Link to Flux guides from the Flux scripting language section

@sanderson is already working on this.

Since Aug 2, 2021.

**The issue:**

Recently, I wanted to find some Flux "guides" -- code samples of how to accomplish common tasks. So, I looked in the left-hand nav of our doc, clicked "[Flux language](https://docs.influxdata.com/influxdb/cloud/reference/flux/)", and found... nothing to help me accomplish my task.

To be clear, the content there is good: list of all functions, the language spec, and Flux vs. InfluxQL. But I was looking for a list of Flux code samples that I could steal from to accomplish some programming tasks.

**My proposal:**

In the [Flux language](https://docs.influxdata.com/influxdb/cloud/reference/flux/) language of the doc, link to the various samples of Flux code sprinkled throughout the doc:

- [Get started with Flux](https://docs.influxdata.com/influxdb/cloud/query-data/get-started/)
- [Query with Flux](https://docs.influxdata.com/influxdb/cloud/query-data/flux/)
- [Common Flux queries](https://docs.influxdata.com/influxdb/cloud/query-data/common-queries/compare_last_measurement/)
- [Downsample data with Flux](https://docs.influxdata.com/influxdb/cloud/process-data/common-tasks/downsample-data/)
- [Send alert emails with Flux](https://docs.influxdata.com/influxdb/cloud/monitor-alert/send-email/)
- [Common alerting tasks in Flux](https://gist.github.com/wolffcm/47f6fac9e2b707c32149caad7f0ecd44), assuming that content gets into our own documentation per [this issue](https://github.com/influxdata/docs-v2/issues/2235).
- [Create custom checks with Flux](https://docs.influxdata.com/influxdb/cloud/monitor-alert/custom-checks/)
- [Monitor states with Flux](https://docs.influxdata.com/influxdb/cloud/monitor-alert/custom-checks/)

This will help make it easier for users to find all the great Flux content that's been written thus far.

##### Relevant URLs
- https://docs.influxdata.com/influxdb/cloud/reference/flux/