Replace commitDate format to ISO8601

[palindrom615]

According to git document, git is using unique datetime format with --iso option.

Replacing it with strict ISO8601 format will improve usability.

[CLAassistant]

All committers have signed the CLA.

[ikhoon]

Replacing it with strict ISO8601 format will improve usability.

@palindrom615 May I know what usability is improved? For humans, --iso would be better for readability.
I am asking because this change could break the parsing logic of versions.properties in Armeria.
https://github.com/line/armeria/blob/2e99b180518f2543c9189a1fe00d5a711a4a7a49/core/src/main/java/com/linecorp/armeria/common/util/Version.java#L202-L204

[palindrom615]

@ikhoon I see. that should not break anything. WDYT about adding commitISODate property as in 6b12c4e?

@palindrom615 May I know what usability is improved? For humans, --iso would be better for readability.

It saves some codes for parsing dateformat. For instance, jib uses iso8601.

jib {
    ...

    container {
        // depends on `common-git.gradle`
        if (
            project.ext.has("repoStatus") &&
            (project.ext.get("repoStatus") as Map<String, Any>)["repoStatus"] as String == "clean"
        ) {
            val repoStatus = project.ext.get("repoStatus") as Map<String, String>
            val commitISODate = repoStatus.get("commitISODate")
            creationTime.set(commitISODate)
        }
    }
}

[ikhoon]

WDYT about adding commitISODate property as in 6b12c4e?

Sounds good. I think we can keep both of them for a while and then deprecate and remove commitDate when all usages are migrated.

Would you be interested in sending a PR to Armeria as well when this PR is merged?

[ikhoon]

Thanks, @palindrom615!

[palindrom615]

Would you be interested in sending a PR to Armeria as well when this PR is merged?

sure I can 🙇

[trustin]

Sounds like a good idea. Thanks, @palindrom615 🙇

[minwoox]

Thanks, @palindrom615!

[minwoox]

@jrhee17 Do you mind reviewing this PR? >_<