config.yaml includes explicit container versions, maybe it should not

[rfay]

What happened (or feature request):

• config.yaml (as created by ddev config includes explicit web and nginx image versions.
• If you leave those explicit definitions out, then the versions specified by ddev are used by all commands.
• If you ddev config with an existing project, all the container versions are updated (whether or not they were empty before).

There are a number of good things about this approach:

• If people check in or otherwise respect.ddev/config.yaml, they can expect ddev behavior to be unchanged and unaffected by ddev version upgrades.

Bad things about this approach:

• ddev upgrades don't automatically result in the required upgrade for the project. This can occasionally be bad, when ddev expects a new behavior and the older container doesn't provide it, or when the user is expecting to automatically have new ddev features.

Paths forward:

• Leave as is
• Stop unconditionally writing the version to config.yaml (but respect if it's there).

I would prefer to go forward with not populating those in the .config.yaml, but providing them as commented-out options. The related problem is that we need to rewrite docker-compose.yml all the time (on every start) to properly respect ddev and container upgrades.

This is closely related to our long-running discussion about who owns what in .ddev.

What you expected to happen:

How to reproduce this:

Version: Please include the output of ddev version, docker version and the project's .ddev/config.yaml.

Anything else do we need to know:

Related source links or issues:

Please use a complexity rating of 1-5 (5 is high) for a feature request. (High complexity implies more PR planning)