Add Attributes from the GUI

[AndreQuimper]

• I have reviewed the OFRAK contributor guide and attest that this pull request is in accordance with it.
• I have made or updated a changelog entry for the changes in this pull request.

One sentence summary of this PR (This should go in the CHANGELOG!)
Added add_attribute and get_all_resource_attributes endpoints to server.py and Button/View to GUI to allow adding ResourceAttribtues manually from GUI, supporting certain workflows like flash unpacking (#573)

Link to Related Issue(s)
#573

Please describe the changes in your request.
Added a button to the AttributesView that displays a view that allows users to manually add ResourceAttributes through the GUI. There is a dropdown menu that lists all resource attributes for ease of selection (with hotkeys for search). Nested attributes can be added through a JSON text input. AttributesView updates automatically after new attributes are added.

Much of the code is largely based on that for the Add Tag functionality, including code in remote_resource.js and AddAttributesView.svelte (mirrors AddTagView.svelte)

Besides unit tests, for manual testing using flash_test_plain.bin do:

1. Add FlashResource tag using toolbar button
2. Add FlashAttributes using new button/view and the following JSON to configure for the test image:

{
    "data_block_format": [
      ["ofrak.core.flash.FlashField", {"field_type": "ofrak.core.flash.FlashFieldType.DATA", "size": 223}],
      ["ofrak.core.flash.FlashField", {"field_type": "ofrak.core.flash.FlashFieldType.ECC", "size": 32}]
    ],
    "ecc_attributes": ["ofrak.core.flash.FlashEccAttributes", 
       {"ecc_class": ["ofrak.core.ecc.reedsolomon.ReedSolomon", {"nsym": 32}]}
    ]
}

3. Unpack now works for Flash image.

Anyone you think should look at this, specifically?
@whyitfor