Rename Filter to MetadataFilter for clarity

[aulorbe]

Problem

Currently, Filter's function is confusing as it relates to Metadata (see this comment for more info).

Solution

Rename Filter to MetadataFilter to convey that it holds metadata that is used to constrain query-related requests.

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update
• Infrastructure change (CI configs, etc)
• Non-code change (docs, etc)
• None of the above: (explain here)

Test Plan

CI passes.

[austin-denoble]

Thanks! LGTM 🚢