cert-manager update policy

[nicks]

Right now, the cert-manager extension defaults to v1.3.1

This is quite old! As @lentzi90 points out - #346

what should be our policy for updating it? Possibilities:

• We should always update the default to the latest cert-manager version ASAP
• Making a "default" version was a huge mistake, and we should change the extension to require the end-user to pass a default
• Something else?

Hopefully this will be a less fraught question as more users pin the version of the extensions repo they're using (as in https://docs.tilt.dev/extensions.html)

This issue is to collect ideas/feedback/proposals.

[lentzi90]

Thanks for creating this issue!
My 2 cents would be to always updated the default to the latest cert-manager version. I think this would be a good for two reasons:

1. It would hopefully make people aware (since it changes all the time) that it is a good idea to specify the version instead of just going with the default.
2. We avoid accidentally exposing users to unsafe/deprecated versions that may have been fixed in newer versions.