Create IClusterConnectionRecord factory with URL-like input and use it in user-facing places

Follow-on to #5745

Anywhere a user can specifiy a cluster file or seed cluster file, such as the environment or a command line argument, should be handled by a factory function that takes a string and instantiates the correct type of IClusterConnectionRecord.

A URL-like scheme would make it possible to easily support the current behavior for backward compatibility but as well as new implementations of the class, for example

```
# path to a file, current behavior, now ClusterConnectionFile

# explicit version of current behavior
file://

# interface for ClusterConnectionMemoryRecord
memory://

# interface for ClusterConnectionKey
fdbkey://

# Future ideas
https://
s3://
azure://
```

No files, tests, or entry points are named. Trace where users provide cluster files or seed cluster files through environment settings and command-line arguments, then determine how those inputs currently become IClusterConnectionRecord instances. Done means a string factory supports the stated path, file://, memory://, and fdbkey:// forms and is used in those user-facing places.

Written by the indexing model from the issue text.