Add proposal SOAR-0008: OpenAPI document filtering (#303)

### Motivation

We'd like to run a proposal for filtering the OpenAPI document for just
the required parts prior to generating.

### Modifications

- Add SOAR-0008: OpenAPI document filtering

(See the proposal itself for details)[^1]

### Result

n/a

### Test Plan

n/a

### Related Issues

#285

[^1]: https://github.com/apple/swift-openapi-generator/pull/303/files

---------

Signed-off-by: Si Beaumont <beaumont@apple.com>

Author: simonjbeaumont

Sources/swift-openapi-generator/Documentation.docc/Proposals/Proposals.md

@@ -49,3 +49,4 @@ If you have any questions, tag [Honza Dvorsky](https://github.com/czechboy0) or
 - <doc:SOAR-0004>
 - <doc:SOAR-0005>
 - <doc:SOAR-0007>
+- <doc:SOAR-0008>

Sources/swift-openapi-generator/Documentation.docc/Proposals/SOAR-0001.md

@@ -6,7 +6,7 @@ Improved mapping of OpenAPI identifiers to Swift identifiers.
 
 - Proposal: SOAR-0001
 - Author(s): [Denil](https://github.com/denil-ct)
-- Status: **In Preview**
+- Status: **Accepted, available since 0.2.0.**
 - Issue: https://github.com/apple/swift-openapi-generator/issues/21
 - Implementation:
     - https://github.com/apple/swift-openapi-generator/pull/89

Sources/swift-openapi-generator/Documentation.docc/Proposals/SOAR-0002.md

@@ -6,7 +6,7 @@ Improved naming of content types to Swift identifiers.
 
 - Proposal: SOAR-0002
 - Author(s): [Honza Dvorsky](https://github.com/czechboy0)
-- Status: **In Preview**
+- Status: **Accepted, available since 0.2.0.**
 - Issue: N/A, was part of multiple content type support: [apple/swift-openapi-generator#6](https://github.com/apple/swift-openapi-generator/issues/6) and [apple/swift-openapi-generator#7](https://github.com/apple/swift-openapi-generator/issues/7)
 - Implementation:
     - [Landed behind a feature flag as part of apple/swift-openapi-generator#146](https://github.com/czechboy0/swift-openapi-generator/blob/4555f8e998b24aa65a462a63828d9195c50dcc23/Sources/_OpenAPIGeneratorCore/Translator/Content/ContentSwiftName.swift#L23-L42)

Sources/swift-openapi-generator/Documentation.docc/Proposals/SOAR-0003.md

@@ -6,7 +6,7 @@ Generate a dedicated Accept header enum for each operation.
 
 - Proposal: SOAR-0003
 - Author(s): [Honza Dvorsky](https://github.com/czechboy0), [Si Beaumont](https://github.com/simonjbeaumont)
-- Status: **In Preview**
+- Status: **Accepted, available since 0.2.0.**
 - Issue: [apple/swift-openapi-generator#160](https://github.com/apple/swift-openapi-generator/issues/160)
 - Implementation:
     - [apple/swift-openapi-runtime#37](https://github.com/apple/swift-openapi-runtime/pull/37)

Sources/swift-openapi-generator/Documentation.docc/Proposals/SOAR-0004.md

@@ -6,7 +6,7 @@ Represent HTTP request and response bodies as a stream of bytes.
 
 - Proposal: SOAR-0004
 - Author(s): [Honza Dvorsky](https://github.com/czechboy0)
-- Status: **Ready for Implementation**
+- Status: **Accepted, available since 0.3.0.**
 - Issue: [apple/swift-openapi-generator#9](https://github.com/apple/swift-openapi-generator/issues/9)
 - Implementation:
     - [apple/swift-openapi-generator#245](https://github.com/apple/swift-openapi-generator/pull/245)

Sources/swift-openapi-generator/Documentation.docc/Proposals/SOAR-0005.md

@@ -6,7 +6,7 @@ Adopt the new ecosystem-wide Swift HTTP Types package for HTTP currency types in
 
 - Proposal: SOAR-0005
 - Author(s): [Honza Dvorsky](https://github.com/czechboy0)
-- Status: **Ready for Implementation**
+- Status: **Accepted, available since 0.3.0.**
 - Issue: [apple/swift-openapi-generator#101](https://github.com/apple/swift-openapi-generator/issues/101)
 - Implementation:
     - [apple/swift-openapi-generator#245](https://github.com/apple/swift-openapi-generator/pull/245)

Sources/swift-openapi-generator/Documentation.docc/Proposals/SOAR-0007.md

@@ -7,7 +7,7 @@ operation outputs.
 
 - Proposal: SOAR-0007
 - Author(s): [Si Beaumont](https://github.com/simonjbeaumont)
-- Status: **Implemented**
+- Status: **Accepted, available since 0.3.0.**
     - Review period: 2023-09-22 – 2023-09-29
     - [Swift Forums post](https://forums.swift.org/t/proposal-soar-0007-shorthand-apis-for-inputs-and-outputs/67444)
 - Issue: