Merge #20090: [doc] Tiny followups to new getpeerinfo connection type field

41dca087b7 [trivial] Extract connection type doc into file where it is used. (Amiti Uttarwar)
3069b56a45 [doc] Improve help for getpeerinfo connection_type field. (Amiti Uttarwar)

Pull request description:

  two commits addressing small followups from #19725

  * first commit adds a clarification in the release notes that this field shouldn't be expected to be stable (suggested by sdaftuar in https://github.com/bitcoin/bitcoin/pull/19725#issuecomment-697421878)

  * second commit moves the `CONNECTION_TYPE_DOC` object out of the header file to reduce the size of the binary (suggested by MarcoFalke in https://github.com/bitcoin/bitcoin/pull/19725#discussion_r495467895, he tested and found a decrease of 10kB)

ACKs for top commit:
  achow101:
    ACK 41dca087b7
  laanwj:
    Code review ACK 41dca087b7

Tree-SHA512: a555df978b4341fbe05deeb40a8a655f0d3c5c1c0adcc1737fd2cf61b204a5a24a301ca0c2b5a3616554d4abf8c57074d22dbda5a50d8450bc22c57679424985

src/net.h

@@ -115,17 +115,12 @@ struct CSerializedNetMsg
     std::string m_type;
 };
 
-const std::vector<std::string> CONNECTION_TYPE_DOC{
-    "outbound-full-relay (default automatic connections)",
-    "block-relay-only (does not relay transactions or addresses)",
-    "inbound (initiated by the peer)",
-    "manual (added via addnode RPC or -addnode/-connect configuration options)",
-    "addr-fetch (short-lived automatic connection for soliciting addresses)",
-    "feeler (short-lived automatic connection for testing addresses)"};
-
 /** Different types of connections to a peer. This enum encapsulates the
  * information we have available at the time of opening or accepting the
- * connection. Aside from INBOUND, all types are initiated by us. */
+ * connection. Aside from INBOUND, all types are initiated by us.
+ *
+ * If adding or removing types, please update CONNECTION_TYPE_DOC in
+ * src/rpc/net.cpp. */
 enum class ConnectionType {
     /**
      * Inbound connections are those initiated by a peer. This is the only