feat: add coverage scripts

[EshaanAgg]

Description

Edited the Makefile to add three new scripts:

• coverage: This target runs the tests and generates a coverage report in the coverage.out file. It utilizes the go test command with the -coverprofile flag to collect coverage data.
  It can be run as make PACKAGE=<path to go package> coverage
  After running the same, the browser shows an HTML page indicating the current coverage.
  

• coverage-clean: This target removes the generated coverage file (coverage.out). It's useful for cleaning up after running coverage tests.

• coverage-help: This target displays a usage message with information about available options and commands related to coverage.

Related Issue(s)

Fixes #15003

Checklist

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[VaibhavMalik4187]

I use the following alias to check to code coverage of any go package:
alias check_coverage="go test ./... -coverprofile=cover.out && go tool cover -html=cover.out -o coverage.html && rm cover.out && firefox coverage.html"
It is very flexible and can be used in any repository and in any directory without specifying the package name. I wonder if suggesting contributors to use a similar alias would be a better idea.

[EshaanAgg]

Seems cool, but how would you customize the package that you want to test and see the reports for with this alias? Running the tests for all the packages every time is not feasible.

[frouioui]

This feels very similar to the already existing unit_test_cover Makefile target. The following snippet is going to be important is testing the sqlparser package:

# Handle go tool cover failures due to not handling `//line` directives, which
# the goyacc compiler adds to the generated parser in sql.go. See:
# https://github.com/golang/go/issues/41222
sed -i'' -e '/^vitess.io\/vitess\/go\/vt\/sqlparser\/yaccpar/d' coverage.out

[EshaanAgg]

Ahh got it. Should I rename the same to test.coverage to avoid the target conflict?

[Maniktherana]

Just a thought, but I often find myself using the -v flag too as it helps find failing tests. Might be worth adding

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