Update package-registry to use EPR production as proxy

[mrodm]

This PR updates the Dockerfile that creates the Elastic Package Registry image to configure the Elastic Package Registry production DNS (https://epr.elastic.co) to be used as proxy. Currently, the default value used is the snapshot one (https://epr-snapshot.elastic.co)

[elasticmachine]

💚 Build Succeeded

the below badges are clickable and redirect to their specific view in the CI or DOCS

Expand to view the summary

Build stats

• Start Time: 2022-10-25T08:39:39.757+0000

• Duration: 33 min 51 sec

Test stats 🧪

Test	Results
Failed	0
Passed	854
Skipped	0
Total	854

🤖 GitHub comments

Expand to view the GitHub comments

To re-run your PR in the CI, just comment with:

• /test : Re-trigger the build.

[elasticmachine]

🌐 Coverage report

Name	Metrics % (covered/total)	Diff
Packages	100.0% (35/35)	💚
Files	66.667% (86/129)	👍
Classes	61.413% (113/184)	👍
Methods	47.52% (364/766)	👍
Lines	30.723% (3288/10702)	👍
Conditionals	100.0% (0/0)	💚

[jsoriano]

Is it needed if we are going to change the default in package-registry itself?

[mrodm]

I just add it in case we want to push this change quick into elastic-package.

This is not totally mandatory, if we can wait until the package-registry release and the required update here in elastic-package (update the docker image used for package-registry - https://github.com/elastic/elastic-package/blob/main/internal/profile/static.go#L126).

I'll keep the PR opened in case we see it is worthy.