Executor configuration extended ..

[milenkovicm]

... this provide much more options to configure executors.

Which issue does this PR close?

Closes #1098.

Rationale for this change

expose more configuration options for executor and scheduler, this way users can set up their own instances with custom configuration (object stores, configuration, udfs ...)

What changes are included in this PR?

• Integration tests have been added which rely on testcontainers infrastructure, thus docker is required for builds. Tests are disabled by default but can be enabled with testcontainers option
• BALLISTA_PLANNER_OVERRIDE config was removed, there is equivalent method in SessionConfigExt
• BallistaFunctionRegistry was promoted a bit, cleaning up executor code
• executor code cleanup

to follow up

• session cofiguration to be propagated from scheduler to executor
• configuration clean up

Are there any user-facing changes?

there are slight changes in original API, but not drastic

[milenkovicm]

will be finalised once #1096 gets merged

[milenkovicm]

SessionContextExt finally provides enough configuration options, getting one step closer to ballista library. I will follow up with documentation update reflecting new interface and removal of object stores.

please have a look when you get chance @andygrove

[andygrove]

LGTM. Thanks @milenkovicm

[milenkovicm]

Thanks @andygrove, I need another pass to clean it up and put documention. Will let you know when ready

[milenkovicm]

i believe this is ready now @andygrove
thanks for your patience