Change b.axialExpTargetComponent to block parameter

[albeanth]

Description

Downstream analysis identified an issue where the blueprints specified axial expansion target component was unable to be used with database loads (i.e., restarts and snapshot runs). This PR changes the Block class instance variable, b.axialExpTargetComponent, to a registered block parameter that gets written to the db.

When a standard run to executed, the axial expansion target components for each block are stored as block parameters and written to the DB. When used for a DB load case, they are directly read off of the database.

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Checklist

• This PR has only one purpose or idea.
• Tests have been added/updated to verify that the new/changed code works.

• The code style follows good practices.
• The commit message(s) follow good practices.

• The release notes (location doc/release/0.X.rst) are up-to-date with any bug fixes or new features.
• The documentation is still up-to-date in the doc folder.
• The dependencies are still up-to-date in setup.py.

[albeanth]

Found an issue with this. Will reopen when ready.

[albeanth]

Found an issue with this. Will reopen when ready.

Note to reviewers: The issue was that originally, b.p.axialExpTargetComponent was storing the Component directly. That caused problems when writing out to the DB. To resolve this, I changed it to store the Component.name instead. I was able to confirm that by making this change and changing the default value from None to "", b.p.axialExpTargetComponent is written as expected. It should be represented the same way b.p.type is represented.

[albeanth]

Coverage failure seems to be coverage spray....

@john-science

[albeanth]

Converting to draft while this waits it's turn in line within a downstream ARMI app.