docs: Repair links to official docs

[bdrianw]

The outdated docs link in cloudnative-pg/cloudnative-pg#9548 is also present in the footer of the CNPG site, and in a few blogposts as well.

[jsilvela]

one loose thing in the hasura post, otherwise looks good

[jsilvela]

Here too. Suggest to use permalink from top repo.

Suggested change

	$ kubectl apply -f https://github.com/cloudnative-pg/cloudnative-pg/blob/c0d218b8f9c68d08e720114b9cc44a1ebad5c46e/docs/src/samples/cluster-example.yaml
	cluster.postgresql.cnpg.io/cluster-example created

[bdrianw]

Good catch, thanks. I think it has to be a raw yaml, rather than the rich github page - the given command fails on a local kind 1.35 cluster with

$ kubectl apply -f https://github.com/cloudnative-pg/cloudnative-pg/blob/c0d218b8f9c68d08e720114b9cc44a1ebad5c46e/docs/src/samples/cluster-example.yaml
error: error parsing https://github.com/cloudnative-pg/cloudnative-pg/blob/c0d218b8f9c68d08e720114b9cc44a1ebad5c46e/docs/src/samples/cluster-example.yaml: error converting YAML to JSON: yaml: line 35: mapping values are not allowed in this context

Also, given that the blogpost is written with fixed references to 1.20 elsewhere (L45-49) I thought it might be best to go with https://raw.githubusercontent.com/cloudnative-pg/cloudnative-pg/refs/heads/release-1.20/docs/src/samples/cluster-example.yaml

I've pushed 7c536e3 with this change (and confirmed the command works with local kind), but let me know if you prefer differently. (Also re-did the commits with -s to address the failing DCO check)

[jsilvela]

Oh and please @bdrianw sign your commit. See the failing DCO check.