Relays: Always respect user's local relay list when present

This commit fixes an issue where the Damus relay (Or other bootstrap relays) would be added to the user's relay list even though they explicitly removed it.

The root cause of the issue lies in the way we load bootstrap relays. The default bootstrap relays would be initially loaded even though the user already has a bootstrap list stored, just in case all the relays on the user list fails. This would cause the app to inadvertently connect to relays that the user did not select whenever there is a connectivity issue with all their listed relays.

The fix is to simply not add the default bootstrap list when the user already has a list stored. We do not need to use bootstrap relays in order to get our relay list, because that list is already stored in both UserDefaults as well as on NostrDB through the user's contact list event. (A contact list which is also locally loaded on startup since the fix related to https://github.com/damus-io/damus/issues/2057)

Issue reproduction + Testing
----------------------------

Procedure:
1. Disconnect from all relays, and disconnect from the Damus relay last.
2. Connect to a local relay (that you control). Connection should be successful.
3. Quit the app completely.
4. Stop the local relay.
5. Restart the app.
6. Go to the relay list view.
7. Check the relay list. It should list the one local relay selected by the user

Issue reproduction:
- Device: iPhone 15 simulator
- iOS: 17.4
- Damus: 1.8 (`97169f4fa276723bfab28ca304953ec206c904d2`)
- Result: ISSUE REPRODUCED
- Details: On step 7, the relay list only lists the Damus relay

Fix test:
- Device: iPhone 15 simulator
- iOS: 17.4
- Damus: This commit
- Result: PASS
- Details: On step 7, the local relay is listed even though connection is unsuccessful. No notes are loaded since no relays were able to connect successfully

Quick regression check
----------------------

PASS

Device: iPhone 15 simulator
iOS: 17.4
Damus: This commit
Steps:
1. Reinstall app from scratch
2. Create a new account, go through onboarding
3. Make sure that new account connects to bootstrap relays. PASS
4. Sign out
5. Sign in with previously existing account (The one from the previous test) (Notice no UserDefaults exists for this user at that point)
6. Make sure relay list is loaded to the latest relay list known to the bootstrap relays (i.e. connects only to the Damus relay) (It cannot recover the latest relay list pointing only to the local relay, since the bootstrap relays have no knowledge about that relay or the contact lists stored there.). PASS

Note: The behavior on step 6 is not a bug, it is an expected limitation. In fact, this behavior is privacy protecting, as the user may not want those public relays from knowing about its connection preference to the local relay (and its address)

Other information
------------------

Q: How is this test using local relays related or equivalent to Tor relay list described in #2186?
A: Those Tor relays need dedicated software (such as Orbot VPN) to be running successfully in order for Damus to make a successful connection to them. If at any moment that VPN stops working, it would trigger the same situation as described in the test above, where all relay connections fail at once.

Q: In #2186, the user reports that the Damus relay is added, but does not describe the Damus relay replacing existing relays. What is the difference?
A: I believe the difference is in the order in which relays are added or removed. We have to remember that the relay we just disconnected from will likely still have version N-1 of our contact list event, where it still includes itself on that list.

Changelog-Fixed: Fix issue where bootstrap relays would inadvertently be added to the user's list on connectivity issues
Closes: https://github.com/damus-io/damus/issues/2186
Signed-off-by: Daniel D’Aquino <daniel@daquino.me>
Reviewed-by: William Casarin <jb55@jb55.com>

damus/Util/Relays/RelayBootstrap.swift

@@ -58,7 +58,7 @@ func load_bootstrap_relays(pubkey: Pubkey) -> [RelayURL] {
 
     let relay_urls = relays.compactMap({ RelayURL($0) })
 
-    let loaded_relays = Array(Set(relay_urls + get_default_bootstrap_relays()))
+    let loaded_relays = Array(Set(relay_urls))
     print("Loading custom bootstrap relays: \(loaded_relays)")
     return loaded_relays
 }