Switch occurrences of master to main

[allisonchou]

Switches master -> main throughout the repo.

Some URLs to other repositories are broken, but I think this should be OK because those specific repos are scheduled to also switch from master to main this sprint.

[dibarbet]

I see a bunch of changes to scripts in eng/common which is managed by arcade. Should we be changing anything there? Seems like we might end up breaking a bunch of stuff. Should those changes be excluded and have arcade branch changes come whenever they push an arcade update to switch over to main?

[allisonchou]

@dibarbet Thanks for the catch! I removed all changes to files in eng/common.

[Youssef1313]

@allisonchou Can you take a look at:

https://github.com/dotnet/arcade-services/blob/737108990a317c591d6beb46197a1b094e5979a6/src/Microsoft.DotNet.Darc/tests/Microsoft.DotNet.Darc.Tests/inputs/DependencyFlowGraph/IncludeBuildTimes/output.json#L489-L490

(I don't know if this requires any action)

[allisonchou]

@Youssef1313 Thanks for the heads up. I opened an issue on the arcade side: dotnet/arcade#7052