Move TriggeredDeploymentID metadata key to command model

[khanhtc1202]

What this PR does / why we need it:

triggeredDeploymentIDKey used in both trigger(piped) and pipectl but must be defined to use could lead to unexpected error in case the key name changed in one end. This PR moves the key to the Command model (since it is the key in command metadata) and explicitly refers it in the used end.

Which issue(s) this PR fixes:

Fixes #

Does this PR introduce a user-facing change?:

NONE

[pipecd-bot]

Some issues were detected while linting go source files in your changes.

[pipecd-bot]

Code coverage for golang is 31.91%. This pull request does not change code coverage.

[nakabonne]

Even if the size of PR is tiny, It would help us to understand what context is behind that if you could write a short note in the PR body. Just a little bit is enough 🙏

[khanhtc1202]

Even if the size of PR is tiny, It would help us to understand what context is behind that if you could write a short note in the PR body. Just a little bit is enough 🙏

Sure, updated the PR description 🙏

[nakabonne]

Thank you. Looks neat!
/lgtm

[nghialv]

/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.