Host Split: explicitly log settings and root path

[brettsam]

We'll be rolling out an in-proc/out-of-proc host split in the near future. As we test this on individual stamps during the rollout, we'll need a concise log emitted from the host to let us know if anything appears wrong. This log should contain:

• FUNCTIONS_WORKER_RUNTIME value
• FUNCTIONS_EXTENSION_VERSION value
• ASPNETCORE_IIS_PHYSICAL_PATH value
• The contents of the ScmHostingConfiguration.txt file (which should already be available in IConfiguration.

This log should also have an explicit EventName so it's easy to query.

[brettsam]

A couple extra notes:

• may be able to just use GetCurrentDiretory() instead of the IIS_PHYSICAL_PATH
• should output as json string
• should include a boolean of whether we're in placeholder/standby mode or not