Add Makefile

What does this MR do?

When working with semgrep I found there were a number of commands I ran regularly, some of which are fairly long-winded (specifically running the rspec integration tests in a container).

To rely less on my bash history and make these commands more discoverable to other engineers, this MR adds a Makefile.

To run any of the commands, from your console from within the semgrep project:

make [task]

The tasks available in this MR are:

• make build.image
• make build.image-fips
• make test.integration this command runs the build.image task first
• make test.integration-fips this command runs the build.image-fips task first

What are the relevant issue numbers?

NA

Does this MR meet the acceptance criteria?

• Changelog entry added
• Documentation created/updated for GitLab EE, if necessary
• Documentation created/updated for this project, if necessary
• Documentation reviewed by technical writer or follow-up review issue created
• Tests added for this feature/bug
• Job definition updated, if necessary
  • Auto-DevOps template
  • Job definition example
  • CI Templates
• Conforms to the code review guidelines
• Conforms to the Go guidelines
• Security reports checked/validated by reviewer