chore: update readme and version number to 1.5.0

[patrzhan]

Issue #, if available:

Description of changes:
Bump version # to 1.5.0
Why is this change necessary:
We are releasing a new GDK version and the readme and version should be properly reflected.
How was this change tested:
Install with pip and confirm gdk -v outputs gdk 1.5.0
Any additional information or context required to review the change:

Checklist:

• Updated the README if applicable
• Updated or added new unit tests
• Updated or added new integration tests
• Updated or added new end-to-end tests
• If your code makes a remote network call, it was tested with a proxy
• You confirm that the change is backwards compatible

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (01c7504) 98.04% compared to head (636c186) 98.04%.

Additional details and impacted files

@@             Coverage Diff              @@
##           development     #257   +/-   ##
============================================
  Coverage        98.04%   98.04%           
============================================
  Files               47       47           
  Lines             1838     1838           
============================================
  Hits              1802     1802           
  Misses              36       36           

Flag	Coverage Δ
integ	80.46% <100.00%> (ø)
uat	70.45% <100.00%> (-0.06%)	⬇️
unit	94.23% <100.00%> (ø)

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Files	Coverage Δ
gdk/_version.py	100.00% <100.00%> (ø)

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