Add piped config-data flag

[khanhtc1202]

What this PR does / why we need it:

Sample command would look like

$ piped piped --metrics \
--tools-dir=/tmp/piped-bin \
--config-data="`cat .dev/piped-config.yaml`"

or

$ piped piped --metrics \
--tools-dir=/tmp/piped-bin \
--config-data='{"apiVersion": "pipecd.dev/v1beta1", "kind": "Piped",...}'

or

$ piped piped --metrics \
--tools-dir=/tmp/piped-bin \
--config-data="`echo $CONFIG_DATA`"

Which issue(s) this PR fixes:

Fixes #2392

Does this PR introduce a user-facing change?:

Enable Piped to load configuration via command line argument using --config-data flag

[pipecd-bot]

Code coverage for golang is 32.10%. This pull request does not change code coverage.

[nakabonne]

As I can see the PR body, it's expected to be JSON. In that case, doesn't it have to use MarsharJSON or something like that?

--config-data='{"apiVersion": "pipecd.dev/v1beta1", "kind": "Piped",...}'

[nakabonne]

Alternatively, we can support a kind of like --config-from-stdin.

[khanhtc1202]

As I can see the PR body, it's expected to be JSON. In that case, doesn't it have to use MarsharJSON or something like that?

--config-data='{"apiVersion": "pipecd.dev/v1beta1", "kind": "Piped",...}'

Well, the fact is our config.DecodeYAML use yaml.YAMLToJSON which allow both YAML and JSON as it input. So basically we don't need to use MarsharJSON or something like that here. In case this --config-data flag is used, I think users would happier to pass string value in JSON format here rather than just YAML format (as we know, yaml requires tabs/spaces strictly so inline command with YAML format is not a good idea), and in the scope of writing down some samples, I chose JSON as it's easier to write.

ref: https://github.com/pipe-cd/pipe/blob/master/pkg/config/config.go#L217

[khanhtc1202]

Alternatively, we can support a kind of like --config-from-stdin.

Could you provide samples for that flag, I think this --config-data could handle most of the cases we want already 🤔

[nakabonne]

Well, the fact is our config.DecodeYAML use yaml.YAMLToJSON which allow both YAML and JSON as it input.

Alright, I didn't even know that 👍

Could you provide samples for that flag,

In that case, --config-from-stdin has no sense. Never mind.

[nakabonne]

/lgtm

[nghialv]

Nice add.
/approve

[pipecd-bot]

This pull request is APPROVED by nghialv.

Approvers can cancel the approval by writing /approve cancel in a comment. Any additional commits also will change this pull request to be not-approved.