0.8.0 Remove deprecated `--allow-repo-config` param

what

• Remove deprecated --allow-repo-config param

why

• Flag --allow-repo-config has been deprecated in favor of creating a server-side repo config file that applies the same configuration
• Use a server-side config file and point --repo-config to it

references

• https://github.com/runatlantis/atlantis/releases/tag/v0.7.0
• https://www.runatlantis.io/docs/configuring-atlantis.html
• https://www.runatlantis.io/docs/server-configuration.html
• https://www.runatlantis.io/docs/server-side-repo-config.html
• https://www.runatlantis.io/docs/repo-level-atlantis-yaml.html