Add CodeQL security scan

[amanbrar1999]

Motivation

Follow up to issue open-telemetry/oteps#144

CodeQL is GitHub's static analysis engine which scans repos for security vulnerabilities. As the project grows and we near GA it might be useful to have a workflow which checks for security vulnerabilities with every PR so we can ensure every incremental change is following best development practices. Also passing basic security checks will also make sure that there aren't any glaring issues for our users.

Changes

• This PR adds CodeQL security checks to the repo
• After every run the workflow uploads the results to GitHub. Details on the run and security alerts will show up in the security tab of this repo.

Workflow Triggers

• daily cron job at 12:00am
• workflow_dispatch (in case maintainers want to trigger a security check manually)

This workflow is identical to the one that already exists in the core dotnet repository

cc- @alolita

[codecov]

Codecov Report

Merging #55 (a38dd5c) into master (37ed2cd) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master      #55   +/-   ##
=======================================
  Coverage   66.18%   66.18%           
=======================================
  Files          28       28           
  Lines         766      766           
=======================================
  Hits          507      507           
  Misses        259      259