Default to the default branch

[katia-sentry]

for the first time UX. IF we only have one branch, we default to that

[RulaKhaled]

for the first time UX. IF we only have one branch, we default to that

After some discovery, we always have a default branch set in the coverage page, i don't see a scenario where a branch is not selected, you can always update the default branch using the dashboard and/or it's updated per yaml https://github.com/codecov/worker/blob/2836ea9a5fb386d60773b2ed581540734c02742f/services/yaml/__init__.py#L117, this is covered.

Please let me know if there's a link or a scenario that would cause the select to not use a branch, as this could effect all users not only 1st time experience. cc: @aj-codecov / @codecovdesign

[RulaKhaled]

closed by closing #550