Current implementation can allow tampering and the CTR->GCM exchange can
help to avoid it.
This commits also alters a behaviour where we moved ahead after failing
to decrypt a recovery document. IMHO we can't move ahead as this is a
fatal error.

Signed-off-by: Victor Shyba <victor1984@riseup.net>

Integrated the secrets's JSON key that specifies ciphers into _crypto
and added optional GCM. Also added a test to check if both cipher types
can be imported.

Resolves: #8680
Signed-off-by: Victor Shyba <victor1984@riseup.net>

Resolves: #8668 - client: substitute usage of CTR mode + HMAC by GCM
cipher mode

Signed-off-by: Victor Shyba <victor1984@riseup.net>

Our magic value wasn't being used and were represented as a string.
Refactored it to a constant, increased it's size to 2 bytes and optimzed
is_symmetrically_encrypted to look for the magic and symmetrically
encrypted flag under base64 encoding. Most file types will use this
feature to help identifying themselves, so it got refactored to serve
the purpose it was created.

We aren't testing huge payloads on CI, so it doesn't make sense to
insert docs one by one. 'gatherResults' can speed up bench setup.

AESWriter and HMACWriter are just applying hmac or aes into a flow of
data. Abstracted the application of those operations into a super class
and highlighted just the difference on each implementation.

After adding the streaming decrypt, some classes were doing almost the
same thing. Unified them.
Also fixed some module level variables to upper case and some class name
to camel case.

Unfortunately, if a doc finishes decryption before the previous one we
will still have an issue while inserting. This commits solves it by
adding the parse and decrypt inside of the semaphore.

We are already doing this on encryption, now we can stream also from
decryption. This unblocks the reactor and will be valuable for blobs-io.

We now encode preamble and ciphertext+hmac in two distinct payloads
separated by a space. This allows metadata to be extracted and used
before decoding the whole document.
It also introduces a single packer for packing and unpacking of data
instead of reads and writes. Downside: doc_id and rev are limited to 255
chars now.