Change metadata attribute definition to indexed=false

[clockard]

What does this PR do?

Change metadata attribute definition to indexed=false to match the solr schema field that is created dynamically

Who is reviewing it?

@jrnorth
@vinamartin
@zkirksey

How should this be tested?

Good CI build

Any background context you want to provide?

What are the relevant tickets?

Fixes: #____

Screenshots

Checklist:

• Documentation Updated
• Update / Add Threat Dragon models
• Update / Add Unit Tests
• Update / Add Integration Tests

Notes on Review Process

Please see Notes on Review Process for further guidance on requirements for merging and abbreviated reviews.

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[ahoffer]

Good call.