support for S3 compatible storages

[alireza-salehi]

Is your feature request related to a problem? Please describe.
cannot use S3 compatible cloud storage, only buckets are listed and plugin cannot read/write to storage.

[02-Aug-2021 08:40:57] 1. Trying to send backup file to S3 Service … [02-Aug-2021 08:40:57] Connected to S3 Bucket "test1" in <LocationConstraint xmlns="http://s3.amazonaws.com/doc/2006-03-01/">default [02-Aug-2021 08:40:57] Checking for not aborted multipart Uploads … [02-Aug-2021 08:40:57] Starting upload to S3 Service … [02-Aug-2021 08:40:57] ERROR: S3 Service API:

Describe the solution you'd like
add an option to "Select a S3 service" list like "Other S3 Compatible"

Describe alternatives you've considered
updraftplus

Additional context
same feature exists in updraftplus, you can get ideas