Update minimum Go version to 1.18

[Zerpet]

At the moment of this writing, supported Go version are 1.18 and 1.19. Golang has a support policy of N-1. From their docs:

Each major Go release is supported until there are two newer major releases.

One benefit of playing this story is a reduced go.sum file, which in turn will "fix" CVEs in security scanners. Note these scanners would report CVEs in old EOL'ed Go versions, the client library code is fine.

In Go 1.18 we can also replace interface{} with any, and explore the option of using generic functions.

[Zerpet]

There are projects out there that bump the Go version in go.mod in minor version releases. I'm inclined to do the same here, instead of waiting for v2. Example: https://github.com/onsi/ginkgo/releases/tag/v2.1.4 onsi/ginkgo@f779385