Add concept page about sampling

[reese-lee]

This takes the first two sections of my tail sampling blog post to start this doc, per this issue #2423.

[reese-lee]

RE: the images -- should I redo this and put it in a directory so I can also store images for this page, or does it make sense to create an img directory in the root of the Concepts directory for all images used in this section?

[chalin]

@reese-lee - for images that appear exclusively in a page, create a page bundle like this:

• Create a directory sample and in it place:
  • The page content inside index.md
  • The various images (directly, not inside an img folder)

I hope that helps. If you'd prefer that I set that up for you, just add the images at the same level as the .md and I'll make relocate & rename files before merging. Let me know.

[reese-lee]

Thank you! I went ahead and did the things. :)

[cartermp]

Overall I think this looks good. There's a lot I'd like to elaborate on for the topic, but it's far better to get this into the docs now than to stress over several more paragraphs of sampling techniques and tradeoffs.

[cartermp]

@reese-lee if you run the prettier formatter over your changes then this will be good to merge.

[chalin]

I rebased, ran the formatter, added a weight (so that the sampling page shows up just before the SDK page) and compressed images. PTAL @reese-lee @cartermp:

• https://deploy-preview-2434--opentelemetry.netlify.app/docs/concepts/sampling/