replace dep with go modules (#16017)

- guide shamelessly stolen from prometheus/prometheus
- updates local interface of oauth exchange
- updates local impl of hclogger
- bump jaeger client version

closes #16088

vendor/github.com/rainycape/unidecode/README.md

@@ -0,0 +1,6 @@
+unidecode
+=========
+
+Unicode transliterator in Golang - Replaces non-ASCII characters with their ASCII approximations.
+
+[![GoDoc](https://godoc.org/github.com/rainycape/unidecode?status.svg)](https://godoc.org/github.com/rainycape/unidecode)