Make kong2tf plugin aware

[mheap]

Automatically generate a konnect_gateway_custom_plugin instance if the provided plugin is not in the list of bundled plugins.

You can update the bundled plugins by running make generate-plugin-list while running a Gateway locally.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 92.00000% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 32.87%. Comparing base (6b96392) to head (0a43b47).
⚠️ Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
kong2tf/generate_resource.go	92.00%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1979      +/-   ##
==========================================
+ Coverage   32.77%   32.87%   +0.10%     
==========================================
  Files          77       77              
  Lines        7046     7064      +18     
==========================================
+ Hits         2309     2322      +13     
- Misses       4543     4546       +3     
- Partials      194      196       +2     

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[harshadixit12]

When a new plugin is introduced in a new kong gateway version - wouldn't the previously released versions of deck treat it as custom plugin

[mheap]

Yes, that's correct. That's the tradeoff we're making (it would still work, just without schema checks in TF)

[harshadixit12]

When we do jsonencode - underlying value of config is a string in https://github.com/Kong/terraform-provider-konnect/blob/main/src/custom_plugin_model.go#L40 - config.String() returns string wrapped in additonal characters, which breaks unmarshal. (ex: output is "\"{\\\"hello\\\":\\\"world\\\"}\"" instead of "{\"hello\":\"world\"}")
We'll need to fix this in custom_plugin_model.go (i'll do it)

I don't think we need to block this PR though.