feat: Hide self-boosts (#3534) (#4101)

# Overview
Some Mastodon posters have a annoying habit of boosting their own posts
some time after they've posted them.
 No need to see the same toot over and over again.

# Changes made
- Add an additional option to the "Filters > Tabs" preference to show
these self-boosts (default: on)
- If "Show boosts" is turned off, self-boosts are automatically hidden.
    
# Screenshot
***screen of "Filters > Tabs" preference***
before | after
:--: | :--:
| <image
src="https://github.com/tuskyapp/Tusky/assets/62137820/16ed2f4a-0776-4f60-afe6-29827acf5bbd"
width="300"> |<image
src="https://github.com/tuskyapp/Tusky/assets/62137820/9d4e1457-f71d-440c-959f-b91f7433b29a"
width="300" />

***screen of Home Timeline***
***switch-on(self-boosts are displayed)*** | ***swith-off(self-boosts
are not displayed)***
:--: | :--:
| <image
src="https://github.com/tuskyapp/Tusky/assets/62137820/3bb80791-a81f-4cbc-98ad-8a14602e53a4"
width="300" />|<image
src="https://github.com/tuskyapp/Tusky/assets/62137820/a7964da8-d106-4209-b911-460ef8988831"
width="300" />

# Related issue
 Fixes #3534

app/src/main/java/com/keylesspalace/tusky/settings/SettingsConstants.kt

@@ -106,6 +106,7 @@ object PrefKeys {
 
     const val TAB_FILTER_HOME_REPLIES = "tabFilterHomeReplies_v2" // This was changed once to reset an unintentionally set default.
     const val TAB_FILTER_HOME_BOOSTS = "tabFilterHomeBoosts"
+    const val TAB_SHOW_HOME_SELF_BOOSTS = "tabShowHomeSelfBoosts"
 
     /** UI text scaling factor, stored as float, 100 = 100% = no scaling */
     const val UI_TEXT_SCALE_RATIO = "uiTextScaleRatio"