Issue 111: option to remove use of waitforit image

[plumdog]

Fixes #111.

• I have filled in the "Changes" section below?
• I have filled in the "How did you test this code" section below?
• I have bumped the version number in /charts/flagsmith/Chart.yaml in the section version or I'm merging to a
  release branch

Changes

Add option to use the waitfordb command from the application Docker image, rather than pulling in a separate image for this purpose.

How did you test this code?

# Default behaviour
$ helm -n flagsmith get values flagsmith-test -o json | jq .api.dbWaiter.useExternalImage
null
# Still uses wait-for-it image
$ kubectl -n flagsmith get deployments.apps -o json | jq -r '[(.items[] | (.spec.template.spec.initContainers // []) | .[].image)] | unique | .[]' 
flagsmith/flagsmith-api:2.42.1
willwill/wait-for-it:latest
...
# With new flag set
$ helm -n flagsmith get values flagsmith-test -o json | jq .api.dbWaiter.useExternalImage
false
# No just the flagsmith API image used
$ kubectl -n flagsmith get deployments.apps -o json | jq -r '[(.items[] | (.spec.template.spec.initContainers // []) | .[].image)] | unique | .[]' 
flagsmith/flagsmith-api:2.42.1

Some considerations:

• default behaviour remains the same
  • this is so users of Flagsmith that do not have waitfordb (believe this is <2.42.0) but using the new chart don't get an error
• still has a wait-for-db init container, rather than relying on the use of waitfordb in run-docker.sh for migrate and serve
  • this is so the value of api.dbWaiter.timeoutSeconds can be supplied to the command

[matthewelwell]

I've aded one comment for discussion and I think we should also consider adding this behaviour to the task processor template?

[matthewelwell]

@plumdog do you want to resolve the conflict and we can merge?

[plumdog]

@matthewelwell done