Fix Bitbucket Cloud Importer

What does this MR do and why?

This MR fixes currently broken Bitbucket Cloud importer. The options hash we pass in that specify correct auth/token urls was not symbolized, resulting in OAuth2 Client to use default settings, instead of the correct ones. OmniAuth::Strategies::Bitbucket.default_options[:client_options].deep_symbolize_keys doesn't symbolize keys (even though I imagine it should), probably because the returned value is not a Hash, but OmniAuth::Strategy::Options. This is why authorize_url is pointing to oauth/authorize instead of what we've set in lib/omni_auth/strategies/bitbucket.rb:14.

22] pry(main)> OmniAuth::Strategies::Bitbucket.default_options[:client_options].class
=> OmniAuth::Strategy::Options
[23] pry(main)> OmniAuth::Strategies::Bitbucket.default_options[:client_options].deep_symbolize_keys
=> {"site"=>"https://bitbucket.org", "authorize_url"=>"https://bitbucket.org/site/oauth2/authorize", "token_url"=>"https://bitbucket.org/site/oauth2/access_token"}
[24] pry(main)> OmniAuth::Strategies::Bitbucket.default_options[:client_options].to_h.deep_symbolize_keys
=> {:site=>"https://bitbucket.org", :authorize_url=>"https://bitbucket.org/site/oauth2/authorize", :token_url=>"https://bitbucket.org/site/oauth2/access_token"}

Mentions #416102 (closed)

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