Update all our `.NET` executables to target `.NET 7.0.x`

This is an issue similar to this one:
- https://github.com/Azure/azure-sdk-tools/issues/4934

but this time we are moving to `.NET 7.0.x`, not `.NET 6.0.x`.

This work was proposed as a result of my conversation with @weshaggard re this PR:
- https://github.com/Azure/azure-sdk-tools/pull/5395

And triggered by @ckairen's attempt to target `.NET 7` in this PR:
- https://github.com/Azure/azure-sdk-tools/pull/5328#pullrequestreview-1290001058

@weshaggard and my general idea is that our executables target framework major version should never differ by more than 1. That is, if our `global.json` lowest supported `.NET` runtime is `6`, the newest any of our tools can target is `7`. If one wants to target `.NET 8`, one first needs to ensure all our projects target at least `.NET 7`. Once this is done, then one can start targeting `.NET 8`.

Thus, given we are about to have first project targeting `.NET 7` due to #5395, I am filling an issue to make everything target `7`.