pkg/naming: shorten regexp when matching many similar names

[abursavich]

Fixes #668.

Pods from a deployment will have long names like:

1. foobar-59c8d74c75-9gv24
2. foobar-59c8d74c75-dhfbj
3. foobar-59c8d74c75-kggvk
4. foobar-59c8d74c75-nd8jm
5. foobar-59c8d74c75-nqctr
6. foobar-59c8d74c75-pxlnd
7. foobar-59c8d74c75-rnxk7
8. foobar-59c8d74c75-rpj7q
9. foobar-59c8d74c75-vl6n6
10. foobar-59c8d74c75-xhvp4

The naive regexp that matches these pods is foobar-59c8d74c75-9gv24|foobar-59c8d74c75-dhfbj|foobar-59c8d74c75-kggvk|foobar-59c8d74c75-nd8jm|foobar-59c8d74c75-nqctr|foobar-59c8d74c75-pxlnd|foobar-59c8d74c75-rnxk7|foobar-59c8d74c75-rpj7q|foobar-59c8d74c75-vl6n6|foobar-59c8d74c75-xhvp4 (len=239).

A shorter regexp that factors out the shared prefixes and matches the same pods is foobar-59c8d74c75-(9gv24|dhfbj|kggvk|n(d8jm|qctr)|pxlnd|r(nxk7|pj7q)|vl6n6|xhvp4) (len=81).

A similar set of only 5 pods achieves 59% compression. This example with 10 pods achieves 66% compression. At 20 pods it's ~71%, at 40 pods it's ~73%, at 80 pods it's ~74%, and at 200 pods it starts to converge to ~75%. The savings ultimately depend on the length of the deployment name, but even pods with short deployment names (e.g. foobar) still benefit because the replicaset hash (e.g. 59c8d74c75) contributes a lot of redundancy.

Instead of trying to implement this transformation directly, this change lets the regexp/syntax package do all the heavy lifting. In some cases this doesn't result in the shortest possible string (e.g. some short prefix repetitions are more optimal than complete prefix factoring: nd8jm|nqctr vs n(d8jm|qctr)), but writing and maintaining a separate implementation isn't worth it to get at these crumbs.

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[dgrisonnet]

I don't see any big issue with that feature. Even if the configuration is templated, I can hardly a scenario where a valid configuration that already expected a regex would break with the simplified version of the expression.

[dgrisonnet]

/assign
/triage accepted

[dgrisonnet]

/ok-to-test

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[abursavich]

/retest

[abursavich]

Hey, @dgrisonnet! Please take another look. Tests are passing.

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