[feature] Add opt-in RSS feed for account's latest Public posts (#897)

* start adding rss functionality

* add gorilla/feeds dependency

* first bash at building rss feed
still needs work, this is an interim commit

* tidy up a bit

* add publicOnly option to GetAccountLastPosted

* implement rss endpoint

* fix test

* add initial user docs for rss

* update rss logo

* docs update

* add rssFeed to frontend

* feed -> feed.rss

* enableRSS

* increase rss logo size a lil bit

* add rss toggle

* move emojify to text package

* fiddle with rss feed formatting

* add Text field to test statuses

* move status to rss item to typeconverter

* update bun schema for enablerss

* simplify 304 checking

* assume account not rss

* update tests

* update swagger docs

* allow more characters in title, trim nicer

* update last posted to be more consistent

internal/processing/account/account.go

@@ -21,6 +21,7 @@ package account
 import (
 	"context"
 	"mime/multipart"
+	"time"
 
 	apimodel "github.com/superseriousbusiness/gotosocial/internal/api/model"
 	"github.com/superseriousbusiness/gotosocial/internal/concurrency"
@@ -53,6 +54,8 @@ type Processor interface {
 	GetLocalByUsername(ctx context.Context, requestingAccount *gtsmodel.Account, username string) (*apimodel.Account, gtserror.WithCode)
 	// GetCustomCSSForUsername returns custom css for the given local username.
 	GetCustomCSSForUsername(ctx context.Context, username string) (string, gtserror.WithCode)
+	// GetRSSFeedForUsername returns RSS feed for the given local username.
+	GetRSSFeedForUsername(ctx context.Context, username string) (func() (string, gtserror.WithCode), time.Time, gtserror.WithCode)
 	// Update processes the update of an account with the given form
 	Update(ctx context.Context, account *gtsmodel.Account, form *apimodel.UpdateCredentialsRequest) (*apimodel.Account, gtserror.WithCode)
 	// StatusesGet fetches a number of statuses (in time descending order) from the given account, filtered by visibility for