Make connection_type for list_connections accept enum values

[maxdeviant]

This PR updates the handling of the connection_type parameter for the sso.list_connections method to support passing a ConnectionType enum value.

To retain backwards compatibility, we attempt to coerce any string values to their corresponding ConnectionType values. If given an invalid string, an exception will be thrown. This should not be a breaking change, as we already validate the connection types on the API side. All we're doing is moving the validation up into the SDK.

Fixes #110.

Closes #111.

[codecov-commenter]

Codecov Report

Merging #112 (5579a73) into master (603da60) will increase coverage by 0.06%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #112      +/-   ##
==========================================
+ Coverage   94.87%   94.93%   +0.06%     
==========================================
  Files          18       18              
  Lines         468      474       +6     
==========================================
+ Hits          444      450       +6     
  Misses         24       24              

Impacted Files	Coverage Δ
workos/sso.py	100.00% <100.00%> (ø)

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