HLA-1207: Add proposal IDs to MVM header keywords

[s-goldman]

Resolves HLA-1207

Closes #1735

This PR adds proposal ids to MVM final product headers. The values are delimited by semicolons and are taken from the hdrtable (extension 4) immediately after the table is created.

I've updated the MVM header rules files for WFC3 and ACS (we are not doing MVMs for WFPC2) so that we now have a Proposal Information section with one entry in extension 0, similar to the lower-level products.

The code change was tested using WFC3/UVIS data in Sextans A (skycell-p1181x15y16) from program 14178 (ippsoot: id1k9w) and program 16104 (ippsoot: iegx03). It was also tested using ACS data in Leo P (skycell-p1715x09y11) using program 13376 (ippsoot: jc9z05) and program 17501 (ippsoot: jf7l05).

Checklist for maintainers

• [x] added entry in CHANGELOG.rst within the relevant release section
• [x] updated or added relevant tests
• [x] updated relevant documentation
• [x] added relevant label(s)