[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.go

@@ -20,6 +20,7 @@ package processing
 
 import (
 	"context"
+	"time"
 
 	apimodel "github.com/superseriousbusiness/gotosocial/internal/api/model"
 	"github.com/superseriousbusiness/gotosocial/internal/gtserror"
@@ -46,6 +47,10 @@ func (p *processor) AccountGetCustomCSSForUsername(ctx context.Context, username
 	return p.accountProcessor.GetCustomCSSForUsername(ctx, username)
 }
 
+func (p *processor) AccountGetRSSFeedForUsername(ctx context.Context, username string) (func() (string, gtserror.WithCode), time.Time, gtserror.WithCode) {
+	return p.accountProcessor.GetRSSFeedForUsername(ctx, username)
+}
+
 func (p *processor) AccountUpdate(ctx context.Context, authed *oauth.Auth, form *apimodel.UpdateCredentialsRequest) (*apimodel.Account, gtserror.WithCode) {
 	return p.accountProcessor.Update(ctx, authed.Account, form)
 }