Update reference data update process

[YingtingChen]

Change Description:

• Added New update process (via WFS) for Admin Bdys layers
• Fixed update process for topo50 layers
• A separate update process (overwrite) for nz coastlines and islands
• Added New update process for NZ Imagery Survey Index
• Added status botton to see if ref data is available for update.

Notes for Testing:

Test the plugin in dev db with the data downloaded in July

Source Code Documentation Tasks:

• README updated (where applicable)
• CHANGELOG (Unreleased section) updated
• Docstrings / comments included to help explain code

User Documentation Tasks:

• Confluence user guide updated (where applicable)

Testing Tasks:

• Added tests that fail without this change
• All tests are passing in development environment
• Reviewers assigned
• Linked to main issue for ZenHub board

[Douglas-K]

All these changes look good and are working well in DEV. This will make it much easier for us to update buildings reference data. Thank you Yingting!