Allow skipping of cog creation

[gadomski]

Related Issue(s):

• Prompted by Document best practice: I/O-free STAC item generation stac-utils/stactools#369

Description:
Adds a cog_hrefs argument to the Ocean Heat Content create_item and cogify functions. In cogify, if a potential new COG's file name matches that of a file name in cog_hrefs, skip creating that cog, and instead point that asset's href to the href in cog_hrefs. This allows for re-generation of the STAC metadata without re-creating the COGs.

We'll eventually have to do the same for the other CDRs but I wanted to start with this one.

PR checklist:

• Code is formatted (run scripts/format).
• Code lints properly (run scripts/lint).
• Tests pass (run scripts/test).
• Documentation has been updated to reflect changes, if applicable.
• Examples do not change, no update required
• Changes are added to the CHANGELOG.

[pjhartzell]

This looks as we discussed earlier.