Remove JobRunners back reference from Job

[potiuk]

This is the final step of decoupling of the job runner from ORM
based BaseJob. After this change, finally we rich the state that
the BaseJob is just a state of the Job being run, but all
the logic is kept in separate "JobRunner" entity which just
keeps the reference to the job. Also it makes sure that
job in each runner is defined as appropriate for each job type:

• SchedulerJobRunner, BackfillJobRunner can only use BaseJob
• DagProcessorJobRunner, TriggererJobRunner and especially the
  LocalTaskJobRunner can keep both BaseJob and it's Pydantic
  BaseJobPydantic representation - for AIP-44 usage.

The highlights of this change:

• Job does not have job_runner reference any more
• Job is a mandatory parameter when creating each JobRunner
• run_job method takes as parameter the job (i.e. where the state
  of the job is called) and executor_callable - i.e. the method
  to run when the job gets executed
• heartbeat callback is also passed a generic callable in order
  to execute the post-heartbeat operation of each of the job
  type
• there is no more need to specify job_type when you create
  BaseJob, the job gets its type by a simply creating a runner
  with the job
• DagFileProcessorManager is now merged into DagProcessorJobRunner.
  The JobRuner was essentially calling the processormanager that
  created processors. In order to make it consistent with other
  Runners - all of it has been moved into runner, so that it
  starts doing "something" - similar as other runners - rather than
  creating processor manager and running it.

This is the final stage of refactoring that was split into
reviewable stages: #30255 -> #30302 -> #30308 -> this PR.

Please check only the last commit.

Closes: #30325

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[potiuk]

I think there are two errors in tests that I will need to fix (let's see for the CI) - but other than that i think this one should be pretty complete and implements what we've been discussing with @mhenc and @vincbeck and @uranusjr before.

[potiuk]

Merged this one into DagProcessorJobRunner - this way it is consistent with other Jobs - which "do something" rather than create another object and "run" it.

[potiuk]

OK. I got it green finally @uranusjr -> this is the target of the refactor, I would love to merge - if possible - the 4 dependent PRs before we cut-off 2.6.0 branch to make cherry-picking easier for 2.6 branch (cc: @jedcunningham, @ephraimbuddy )