Add a config module containing a dataclass
UpdaterConfig with all client settings.
Initialize updater with default settings
if no other condig is provided.

Signed-off-by: Teodora Sechkova <tsechkova@vmware.com>

Since configuration constants are now part of a
config class, make them lower case. This also avoids
pylint's invalid-name error for class attributes.

Remove the 'default' prefix as they are now configurable
options.

Signed-off-by: Teodora Sechkova <tsechkova@vmware.com>

Stop using the settings module and add the RequestsFetcher
specific config as instance attributes.
Users of the requests-based fetcher implementation can
modify them after instantiating a RequestsFetcher
object if needed.

Signed-off-by: Teodora Sechkova <tsechkova@vmware.com>