Support custom s3 endpoint for Match storage

[mattblaq]

Checklist

• I've run bundle exec rspec from the root directory to see all new and existing tests pass
• I've followed the fastlane code style and run bundle exec rubocop -a to ensure the code style is valid
• I've read the Contribution Guidelines
• I've updated the documentation if necessary.

Motivation and Context

Our company no longer exposes git repos (where we were storing mobile certs) to BitRise (where we are running match from). We can, however, store certs on our own instance of Minio, an open source S3, and expose it to BitRise.

Description

This PR adds fastlane match options to support custom S3 endpoints.

Testing Steps

Setup a local Minio server

brew install minio/stable/minio
minio server ~/minio_test_data

Create Minio bucket

brew install minio/stable/mc
mc alias set minio_test http://127.0.0.1:9000 minioadmin minioadmin
mc mb minio_test/mobile-certs

Configure a Matchfile like this:

storage_mode "s3"
s3_endpoint "http://127.0.0.1:9000" # new
s3_access_key "minioadmin"
s3_secret_access_key "minioadmin"
s3_bucket "mobile-certs"
s3_region "us-west-1"
s3_ssl_verify_peer false # new
s3_force_path_style true # new

Run match

bundle exec fastlane match

Check for files with mc ls:

mc ls minio_test/mobile-certs