Pass the correct LDFLAGS when building the operator image

[ChenYi015]

Purpose of this PR

Make LDFLAGS can be passed as expected when run make build-operator.

Proposed changes:

• Update module path in Makefile by fetching it from go.mod file.
• Update .dockerignore to make the git tree status clean when building the docker image.

Change Category

• Bugfix (non-breaking change which fixes an issue)
• Feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that could affect existing functionality)
• Documentation update

Rationale

Checklist

• I have conducted a self-review of my own code.
• I have updated documentation accordingly.
• I have added tests that prove my changes are effective or that my feature works.
• Existing unit tests pass locally with my changes.

Additional Notes

[vara-bonthu]

/lgtm

[ChenYi015]

/approve

[google-oss-prow]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: ChenYi015

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[ChenYi015]

/cherrypick release-2.2

[google-oss-robot]

@ChenYi015: new pull request created: #2544

In response to this:

/cherrypick release-2.2

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