Reject boolean log envvars

[rainest]

What this PR does / why we need it:

Checks the type of any environment variable containing _log. If it is a boolean, emit a failure instructing users to add quotes.

Reverts 2edf22d, which previously addressed this by enforcing string types for all variables.

Which issue this PR fixes

• fixes Validate that env values are strings (and not bools/numbers) #701

Special notes for your reviewer:

In general, we don't care if YAML's stupid type coercion nonsense changes off to false: Pod envvars are ultimately all treated as strings by Kubernetes, and Kong accepts either value for boolean config values.

The various _log variables are a special case: these are not booleans, and the literal string off is a special value that disables logging. YAML nonsense converting these to booleans (and then Kubernetes converting them back to strings) is a problem, since false is valid value for the non-special case of this of setting, where it's instead interpreted as a file path. I'm not entirely sure why using <prefix dir>/false breaks the container (it's a valid path and Kong should be able to write to it fine), but in any case, it's something we can check special for these.

Manual testing

Dunno why --set doesn't work to set the boolean of this for me, so these are in values.yaml files instead. With this change:

17:24:29-0800 esenin $ cat /tmp/values_string_off.yaml
env:
  proxy_access_log: "off"

17:24:34-0800 esenin $ cat /tmp/values_raw_off.yaml   
env:
  proxy_access_log: off

17:24:36-0800 esenin $ helm template --debug bread /tmp/symkong -f /tmp/values_string_off.yaml | grep -A1 PROXY_ACCESS
        - name: KONG_PROXY_ACCESS_LOG
          value: "off"
--
        - name: KONG_PROXY_ACCESS_LOG
          value: "off"

17:25:01-0800 esenin $ helm template --debug bread /tmp/symkong -f /tmp/values_raw_off.yaml                        
Error: execution error at (kong/templates/deployment.yaml:99:12): env.proxy_access_log must use string 'off' to disable. Without quotes, YAML will coerce the value to a boolean and Kong will reject it
helm.go:84: [debug] execution error at (kong/templates/deployment.yaml:99:12): env.proxy_access_log must use string 'off' to disable. Without quotes, YAML will coerce the value to a boolean and Kong will reject it

Checklist

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• PR is based off the current tip of the main branch.
• Changes are documented under the "Unreleased" header in CHANGELOG.md
• Commits follow the Kong commit message guidelines