DiskManager and TempFiles getting created several times per query

[alamb]

Describe the bug
If you run a query in DataFusion against parquet files, it will create several unnecessary temporary files.

IOx also hits the same thing (with the same root cause): https://github.com/influxdata/influxdb_iox/issues/3507#issuecomment-1023679575

There are several places which (non obviously) create a DiskManager instance today -- the one that hits the parquet usecase above is (in the creation of the pruning predicate that requires an ExecutionContext): https://github.com/apache/arrow-datafusion/blob/master/datafusion/src/physical_optimizer/pruning.rs#L132

This has two problems:

1. it is unneeded overhead (the disk manager is not used),
2. the overhead is larger than it needs to be (it creates a tempfile)

I propose a two pronged solution (will propose two PRs):

1. Create temp files on demand in the DiskManger (so we are at least not doing IO unless needed)
2. Remove unnecessary creation of ExecutionContext

I think the second will be a slightly larger project as it gets passed to create_physical_expr

Though I think the main sources of problem are related to create_physical_expr and that only uses the context to look up vars, if necessary.

[alamb]

cc @yjshen I plan to work on these items today