[chore] Update interactionPolicy sub-policy parsing in line with documented defaults (#4229)

# Description

> If this is a code change, please include a summary of what you've coded, and link to the issue(s) it closes/implements.
>
> If this is a documentation change, please briefly describe what you've changed and why.

Brings our parsing of unset sub-policies in line with the defaults documented here: https://docs.gotosocial.org/en/v0.19.1/federation/interaction_policy/#defaults-per-sub-policy

Closes https://codeberg.org/superseriousbusiness/gotosocial/issues/4146

Part of https://codeberg.org/superseriousbusiness/gotosocial/issues/4026

## Checklist

Please put an x inside each checkbox to indicate that you've read and followed it: `[ ]` -> `[x]`

If this is a documentation change, only the first checkbox must be filled (you can delete the others if you want).

- [x] I/we have read the [GoToSocial contribution guidelines](https://codeberg.org/superseriousbusiness/gotosocial/src/branch/main/CONTRIBUTING.md).
- [x] I/we have discussed the proposed changes already, either in an issue on the repository, or in the Matrix chat.
- [x] I/we have not leveraged AI to create the proposed changes.
- [x] I/we have performed a self-review of added code.
- [x] I/we have written code that is legible and maintainable by others.
- [x] I/we have commented the added code, particularly in hard-to-understand areas.
- [ ] I/we have made any necessary changes to documentation.
- [x] I/we have added tests that cover new code.
- [x] I/we have run tests and they pass locally with the changes.
- [x] I/we have run `go fmt ./...` and `golangci-lint run`.

Reviewed-on: https://codeberg.org/superseriousbusiness/gotosocial/pulls/4229
Co-authored-by: tobi <tobi.smethurst@protonmail.com>
Co-committed-by: tobi <tobi.smethurst@protonmail.com>

testrig/testmodels.go

@@ -2245,13 +2245,13 @@ func NewTestStatuses() map[string]*gtsmodel.Status {
 			CreatedWithApplicationID: "01F8MGY43H3N2C8EWPR2FPYEXG",
 			Federated:                util.Ptr(true),
 			InteractionPolicy: &gtsmodel.InteractionPolicy{
-				CanLike: gtsmodel.PolicyRules{
+				CanLike: &gtsmodel.PolicyRules{
 					AutomaticApproval: gtsmodel.PolicyValues{gtsmodel.PolicyValueAuthor},
 				},
-				CanReply: gtsmodel.PolicyRules{
+				CanReply: &gtsmodel.PolicyRules{
 					AutomaticApproval: gtsmodel.PolicyValues{gtsmodel.PolicyValueAuthor},
 				},
-				CanAnnounce: gtsmodel.PolicyRules{
+				CanAnnounce: &gtsmodel.PolicyRules{
 					AutomaticApproval: gtsmodel.PolicyValues{gtsmodel.PolicyValueAuthor},
 				},
 			},
@@ -2428,13 +2428,13 @@ func NewTestStatuses() map[string]*gtsmodel.Status {
 			CreatedWithApplicationID: "01F8MGYG9E893WRHW0TAEXR8GJ",
 			Federated:                util.Ptr(true),
 			InteractionPolicy: &gtsmodel.InteractionPolicy{
-				CanLike: gtsmodel.PolicyRules{
+				CanLike: &gtsmodel.PolicyRules{
 					AutomaticApproval: gtsmodel.PolicyValues{gtsmodel.PolicyValuePublic},
 				},
-				CanReply: gtsmodel.PolicyRules{
+				CanReply: &gtsmodel.PolicyRules{
 					AutomaticApproval: gtsmodel.PolicyValues{gtsmodel.PolicyValueAuthor},
 				},
-				CanAnnounce: gtsmodel.PolicyRules{
+				CanAnnounce: &gtsmodel.PolicyRules{
 					AutomaticApproval: gtsmodel.PolicyValues{gtsmodel.PolicyValuePublic},
 				},
 			},
@@ -2460,14 +2460,14 @@ func NewTestStatuses() map[string]*gtsmodel.Status {
 			CreatedWithApplicationID: "01F8MGYG9E893WRHW0TAEXR8GJ",
 			Federated:                util.Ptr(true),
 			InteractionPolicy: &gtsmodel.InteractionPolicy{
-				CanLike: gtsmodel.PolicyRules{
+				CanLike: &gtsmodel.PolicyRules{
 					AutomaticApproval: gtsmodel.PolicyValues{gtsmodel.PolicyValuePublic},
 				},
-				CanReply: gtsmodel.PolicyRules{
+				CanReply: &gtsmodel.PolicyRules{
 					AutomaticApproval: gtsmodel.PolicyValues{gtsmodel.PolicyValueAuthor},
 					ManualApproval:    gtsmodel.PolicyValues{gtsmodel.PolicyValuePublic},
 				},
-				CanAnnounce: gtsmodel.PolicyRules{
+				CanAnnounce: &gtsmodel.PolicyRules{
 					AutomaticApproval: gtsmodel.PolicyValues{gtsmodel.PolicyValuePublic},
 				},
 			},
@@ -2492,13 +2492,13 @@ func NewTestStatuses() map[string]*gtsmodel.Status {
 			CreatedWithApplicationID: "01F8MGYG9E893WRHW0TAEXR8GJ",
 			Federated:                util.Ptr(false),
 			InteractionPolicy: &gtsmodel.InteractionPolicy{
-				CanLike: gtsmodel.PolicyRules{
+				CanLike: &gtsmodel.PolicyRules{
 					AutomaticApproval: gtsmodel.PolicyValues{gtsmodel.PolicyValuePublic},
 				},
-				CanReply: gtsmodel.PolicyRules{
+				CanReply: &gtsmodel.PolicyRules{
 					AutomaticApproval: gtsmodel.PolicyValues{gtsmodel.PolicyValuePublic},
 				},
-				CanAnnounce: gtsmodel.PolicyRules{
+				CanAnnounce: &gtsmodel.PolicyRules{
 					AutomaticApproval: gtsmodel.PolicyValues{gtsmodel.PolicyValueAuthor},
 				},
 			},