Populate x509.Certificate.Policies field

[Juneezee]

Part of #7148.

Note

Starting from Go 1.24, x509.Certificate.Policies is the default field used for marshalling certificates. golang/go@918765b

[Juneezee]

ZLint still requires the PolicyIdentifiers field to be populated so we cannot drop the PolicyIdentifiers field completely yet.

https://github.com/letsencrypt/boulder/actions/runs/12731876566/job/35486388841#step:6:22:

failed lint(s): e_sub_ca_certificate_policies_missing ()

I have submitted an issue zmap/zlint#910 to ZLint repository.

[aarongable]

This PR does not close #7148. In order to fully complete that ticket, it needs to also address the PolicyIdentifiers/Policies fields during issuance of Subscriber certificates, as well as anywhere else we construct an x509.Certificate. There may be other places I missed, you should search for them.

[Juneezee]

Populated the Policies field in places where PolicyIdentifiers are also populated in commit 4ad9f89.

I performed a search in VSCode and found 8 occurrences of the word PolicyIdentifiers.

[aarongable]

LGTM, I think this approach makes sense. Requesting second review from the team.

[beautifulentropy]

Thanks for the contribution @Juneezee! Overall I think this change looks really good, I have just few suggestions to improve it a little more.

[beautifulentropy]

Just FYI, this PR is now on-hold until we're using Go 1.24 in our go.mod. No further action is required on your end.