csv export: override default max days (default: 90d)

[a7i]

What does this PR change?

• OpenCost docs mention that CSV Export includes previous day data (ref). The query here, however, requests 90d of data which is not allowed by AWS Managed Prometheus (by default). This allows the user to set the duration desired

Does this PR relate to any other PRs?

• No

How will this PR impact users?

• for existing setup, the duration stays as 90d
• if env is set, it will use the duration as provided

Does this PR address any GitHub or Zendesk issues?

• Closes csv export cost model: data query interval should be 1 day instead of 90 days #2164

How was this PR tested?

• Unit test and dev environment

Does this PR require changes to documentation?

• No

Have you labeled this PR and its corresponding Issue as "next release" if it should be part of the next OpenCost release? If not, why not?

• yes

[mattray]

Thanks for the PR (with tests)! I'm going to ping @r2k1 and his team since they wrote the original feature, hopefully he'll weigh in.

[r2k1]

Overall, LGTM. I would only ask to rename the ENV variable.

The 90 days selection was arbitrary, chosen for checking the oldest data in Prometheus. If this causes issues on some Prometheus setups, we can reduce it. I don't anticipate problems with existing deployments. However, reducing this period would affect the data amount exported on initial runs where opencost has been active for extended periods without CSV export.

An alternative is to execute multiple 30-day range queries. This may eliminate the need from users to configure an extra ENV variable.

[mattray]

With @r2k1's approval I'm going to get this lined up for inclusion in 1.107. Thanks!