addmultisigaddress creates an address respecting the setting, being unable to generate a specific type of address without also adding it to the wallet seems wrong.

I suppose in the future `addresstype` may be refactored to be wallet-specific, which would leave this non-wallet rpc call without an argument. Perhaps there should just be an optional parameter to set it.
CFeeRate m_discard_rate{DEFAULT_DISCARD_FEE};
    OutputType m_default_address_type{DEFAULT_ADDRESS_TYPE};
    OutputType m_default_change_type{DEFAULT_CHANGE_TYPE};
    bool NewKeyPool();
    size_t KeypoolCountExternalKeys() EXCLUSIVE_LOCKS_REQUIRED(cs_wallet);
    bool TopUpKeyPool(unsigned int kpSize = 0);
    /**
     * Reserves a key from the keypool and sets nIndex to its index
     *
     * @param[out] nIndex the index of the key in keypool
     * @param[out] keypool the keypool the key was drawn from, which could be the
     *     the pre-split pool if present, or the internal or external pool
     * @param fRequestedInternal true if the caller would like the key drawn
     *     from the internal keypool, false if external is preferred
     *
     * @return true if succeeded, false if failed due to empty keypool
     * @throws std::runtime_error if keypool read failed, key was invalid,
     *     was not found in the wallet, or was misclassified in the internal
     *     or external keypool
     */
    bool ReserveKeyFromKeyPool(int64_t& nIndex, CKeyPool& keypool, bool fRequestedInternal);
    void KeepKey(int64_t nIndex);
    void ReturnKey(int64_t nIndex, bool fInternal, const CPubKey& pubkey);
    bool GetKeyFromPool(CPubKey &key, bool internal = false);
    int64_t GetOldestKeyPoolTime();
    /**
     * Marks all keys in the keypool up to and including reserve_key as used.
     */
    void MarkReserveKeysAsUsed(int64_t keypool_id) EXCLUSIVE_LOCKS_REQUIRED(cs_wallet);
    const std::map<CKeyID, int64_t>& GetAllReserveKeys() const { return m_pool_key_to_index; }