feat: Improve mage coverage command: add -coverpkg option and -func report

[cletter7]

Changes:

• Add -coverpkg ./... option to the mage coverage command
• Add -func report to the mage coverage command

With -coverpkg ./... the total coverage is different, and the -func report includes files with 0% coverage.

Below you can find the coverage diff screenshot from github-datasource.

On the left (without -coverpkg, total coverage 45.5%):

go test ./pkg/... -v -cover -coverprofile=coverage/backend.out && go tool cover -func=coverage/backend.out -o coverage/backend.txt

On the right (with -coverpkg, total coverage 39.9%):

go test ./pkg/... -coverpkg ./... -v -cover -coverprofile=coverage/backend.out && go tool cover -func=coverage/backend.out -o coverage/backend.txt

[CLAassistant]

All committers have signed the CLA.

[andresmgot]

Tested and working as expected for me 👍