[docs] Multiple release prep docs changes, fixes ddev#4411 (ddev#4456)

Bump images to v1.21.3 and mutagen to 0.16.0 (ddev#4310)

Bump mutagen to 0.16.0-rc1 (ddev#4277)

Allow overriding config in `config.*.yaml` using `override_config: tr…

…ue`, fixes ddev#4100, fixes ddev#4079, fixes ddev#4099 (ddev#4118)

Remove nodejs 12 and 17 from allowed values as out of support (ddev#4073

)

Bump images to v1.19.5 (ddev#4011)

Bump docker images for v1.19.4 (ddev#4010)

gitignore /artifacts and do goreleaser before artifacts (ddev#4007)

Support for pre.Dockerfile.* (ddev#3999) fixes ddev#3960, fixes ddev#…

…3988

Don't ask people to ddev poweroff if first use of ddev (ddev#3965)