rcal-845_dsd rename highlevelpipeline to mosaicpipeline

[ddavis-stsci]

Resolves RCAL-845

Closes #1247

This PR renames the highlevel pipeline to mosaic pipeline and updates the documentation to reflect this.

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

The regression tests are passing and are at https://plwishmaster.stsci.edu:8081/job/RT/job/Roman-Developers-Pull-Requests/795/

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 85.71429% with 1 line in your changes missing coverage. Please review.

Project coverage is 78.93%. Comparing base (1aec135) to head (27ec5d7). Report is 187 commits behind head on main.

Files	Patch %	Lines
romancal/pipeline/mosaic_pipeline.py	75.00%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #1249 +/- ## ======================================= Coverage 78.93% 78.93% ======================================= Files 117 117 Lines 8086 8086 ======================================= Hits 6383 6383 Misses 1703 1703 ``` | [Flag](https://app.codecov.io/gh/spacetelescope/romancal/pull/1249/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/1249/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=spacetelescope) | `62.78% <ø> (ø)` | | Carriedforward from [600d00f](https://app.codecov.io/gh/spacetelescope/romancal/commit/600d00f2ccffa4e21847c28277954b0a7dbc1537?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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[schlafly]

Can you also update the make_regtestdata.sh script with roman_hlp -> roman_mos so that we can still build all of the regtest files? Otherwise LGTM, thanks!