Allow SSL support for Sentinel

[n-elloco]

Currently there is no possibility to pass SSL parameters to connect to Sentinel instance and then to connect to the selected Node.

How it will work:

import arq

settings = arq.connections.RedisSettings(
    host=[('localhost', 26379)],  # sentinel host/port
    port=6379,  # node port
    database=1,
    username='redis',  # node user
    password='***',  # node password
    ssl_keyfile='/ssl/client.key',
    ssl_certfile='/ssl/client.crt',
    ssl_ca_certs='/ssl/ca.crt',
    ssl=True,
    sentinel=True,
    sentinel_kwargs=dict(
        username='sentinel',  # sentinel user
        password='***',  # sentinel password
        ssl_keyfile='/ssl/client.key',
        ssl_certfile='/ssl/client.crt',
        ssl_ca_certs='/ssl/ca.crt',
        ssl=True,
    )
)   
pool = await arq.create_pool(settings)

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@@            Coverage Diff             @@
##             main     #506      +/-   ##
==========================================
- Coverage   96.27%   96.10%   -0.17%     
==========================================
  Files          11       11              
  Lines        1074     1079       +5     
  Branches      209      190      -19     
==========================================
+ Hits         1034     1037       +3     
- Misses         19       21       +2     
  Partials       21       21              

Files with missing lines	Coverage Δ
arq/connections.py	87.50% <100.00%> (-2.57%)	⬇️

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[n-elloco]

@samuelcolvin @chrisguidry please, review