Following go1.18 TLS changes

[Julien Pivotto]

Dear developers

Go1.18 changes the default minimum TLS version for the client to TLSv1.2.

Prometheus 2.35 will be built with Go1.18.

I am introducing a setting for users that might be broken by
this upstreamchange:

tls_config:
min_version: TLS10

(TLS10 comes from the way we specify TLS versions in the Exporter
toolkit, which comes from go/crypto variable names).

https://github.com/prometheus/common/pull/375


I am not more clever than the go team in deciding which should be the
default TLS version, and I strongly think that as an industry we need to
move to TLS1.2+. Therefore I plan to leave the go runtime defaults.

Affected users can also set GODEBUG=tls10default=1 for go1.18 to revert this
change temporarily (this workaround will be removed in go1.19).

Regards,

--
Julien Pivotto
@roidelapluie