Rcal 854 Tweakreg step listed as skipped when run & refactor exposure pipeline

[ddavis-stsci]

Resolves RCAL-854

Closes #1263

This PR fixes the error that the tweakreg step is listed as skipped when it is run. This PR also refactors the exposure level pipeline to take advantage of the model container and associations.

Checklist

• [x] added entry in CHANGES.rst under the corresponding subsection
• [x] updated relevant tests
• [x] updated relevant documentation
• [x] updated relevant milestone(s)
• [x] added relevant label(s)
• [x] ran regression tests, post a link to the Jenkins job below. How to run regression tests on a PR https://plwishmaster.stsci.edu:8081/job/RT/job/Roman-Developers-Pull-Requests/828/ The regression test truth data will need updating to fix the tests ( cal_step SKIPPED --> COMPLETE)

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 6.66667% with 14 lines in your changes missing coverage. Please review.

Project coverage is 79.24%. Comparing base (6b1c696) to head (ac77d75).

Files	Patch %	Lines
romancal/pipeline/exposure_pipeline.py	6.66%	14 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #1271 +/- ## ========================================== + Coverage 78.99% 79.24% +0.25% ========================================== Files 117 117 Lines 8101 8075 -26 ========================================== Hits 6399 6399 + Misses 1702 1676 -26 ``` | [Flag](https://app.codecov.io/gh/spacetelescope/romancal/pull/1271/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=spacetelescope) | Coverage Δ | | *Carryforward flag | |---|---|---|---| | [nightly](https://app.codecov.io/gh/spacetelescope/romancal/pull/1271/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=spacetelescope) | `62.78% <ø> (-0.02%)` | :arrow_down: | Carriedforward from [6b1c696](https://app.codecov.io/gh/spacetelescope/romancal/commit/6b1c696b20ae877e61aedd55fec5a6188b0c12d8?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=spacetelescope) | *This pull request uses carry forward flags. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=spacetelescope) to find out more.

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