`ob run` works with `runBackendWith`

[ohri-anurag]

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This PR is meant to resolve the issue #691. ob run was initially using a different code path to run an Obelisk project, which did not honor the BackendConfig passed to runBackendWith, even though the binary generated by building the project was honoring it.

After these changes, ob run also uses the same code as the built binary, and hence honors the settings passed to runBackendWith.

I have:

• [x] Based work on latest develop branch
• [x] Followed the contribution guide
• [x] Looked for lint in my changes with hlint . (lint found code you did not write can be left alone)
• [x] Run the test suite: $(nix-build -A selftest --no-out-link)
• [x] Updated the changelog
• [ ] (Optional) Run CI tests locally: nix-build release.nix -A build.x86_64-linux --no-out-link (or x86_64-darwin on macOS)

[madeline-os]

This change breaks older obelisk projects, because it changes the name of the backend executable main, from main.hs to Main.hs . I will let you know what we should do.