Add variables, templating & fix formatting

[frivoire]

What/Why ?

This PR contains several modest bugfixes & improvements for better customization capabilities.
cf details in each individual commit message (they are pretty autonomous).

Notes

About 1st commit Fix formatting of 'redash.env' function:

It's about fixing a bug in the chart for one specific (non default) use-case: when we using an external postgres + redis.
Basically like this (on master branch) :

$ helm template --set postgresql.enabled=false,redis.enabled=false,externalPostgreSQL=pgConnectionString,externalRedis=redisConnectionString .

Error: YAML parse error on redash/templates/hook-migrations-job.yaml: error converting YAML to JSON: yaml: line 40: block sequence entries are not allowed in this context

And with the --debug option, we can see the issue in the generated yamls:

[...]
       env:
          - name: REDASH_DATABASE_URL
            value: "pgConnectionString"- name: REDASH_REDIS_URL
            value: "redisConnectionString"## Start primary Redash configuration
          - name: REDASH_SECRET_KEY
            valueFrom:
              secretKeyRef:
                name: release-name-redash
                key: secretKey

=> missing new lines

Thus my 1st commit that ensure proper newlines are in place.

NB: I'm seeing just now that a PR already exists for (part of) this issue: #176
I recommend to keep "my" version, because I cover both cases: postgres & redis, not just redis.

About all commits

I compared the generated manifests (using chart's default values) between the "before" and "after" my PR, cf: helm template .
=> no change (except some white-spaces at the end of some lines)

So, it shouldn't create any regression 😃

[frivoire]

Any remark on this PR ?
maybe @justinclift or @lucydodo (active recently here)

[lucydodo]

Sorry, I must have missed the notification. I'm out of town right now, so I'll take a look when I get home in the morning.

[lucydodo]

I had a moment to review this PR.
LGTM. approves this PR. Thank you for contribution. :)

[frivoire]

Sorry, I must have missed the notification

No need to excuse, there is no guarantee on a community project :)

I had a moment to review this PR.
LGTM. approves this PR

Thanks for the review & merge !