update go version to 1.21

[dagbay-rh]

Summary

• update go to version 1.21

Why

We are currently on version 1.19, so this just bumps us up to the current release of go

Testing

• successfully ran go mod tidy and go get ./... and built/ran the service locally via make && make exe
• hit all of our endpoints locally and they all worked fine
• ran unit tests, all work
• pipeline build is successful

[dagbay-rh]

our jenkins nodes might be lacking support for go1.21, pr check failing because of this:

19:25:20 controllers/subscriptions.go:10:2: package slices is not in GOROOT (/usr/lib/golang/src/slices)
19:25:20 note: imported by a module that requires go 1.21
19:25:20 make: *** [test-all] Error 1

[dagbay-rh]

our jenkins nodes the pr check runs on only supports up to go1.20 right now. closing this pr in favor of this new pr to bump us to 1.20 for now: #163