Pv/filter extension conformance class consistency

[philvarner]

Related Issue(s):

• Fix uses of https://api.stacspec.org/v1.0.0-beta.5/item-search#filter:item-search-filter #280
• Fix warnings in filter fragment openapi #281

Proposed Changes:

1. replace uses of https://api.stacspec.org/v1.0.0-beta.5/item-search#filter:item-search-filter with https://api.stacspec.org/v1.0.0-beta.5/item-search#filter
2. Fix a few warnings in the filter openapi b/c the names of tags were wrong

PR Checklist:

• This PR is made against the dev branch (all proposed changes except releases should be against dev, not master).
• This PR has no breaking changes.
• This PR does not make any changes to the core spec in the stac-spec directory (these are included as a subtree and should be updated directly in radiantearth/stac-spec)
• I have added my changes to the CHANGELOG or a CHANGELOG entry is not required.