Update version and changelog for v1.4.0 release

[duckontheweb]

Description:

Updates CHANGELOG and package version for the v1.4.0 release.

PR Checklist:

• Code is formatted (run pre-commit run --all-files)
• Tests pass (run scripts/test)
• Documentation has been updated to reflect changes, if applicable
• This PR maintains or improves overall codebase code coverage.
• Changes are added to the CHANGELOG. See the docs for information about adding to the changelog.

[codecov-commenter]

Codecov Report

Merging #753 (6e9d413) into main (cbf78ab) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main     #753   +/-   ##
=======================================
  Coverage   94.55%   94.55%           
=======================================
  Files          79       79           
  Lines       11621    11621           
  Branches     1370     1370           
=======================================
  Hits        10988    10988           
  Misses        455      455           
  Partials      178      178           

Impacted Files	Coverage Δ
pystac/version.py	100.00% <100.00%> (ø)

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[gadomski]

Changlog has whitespace missing on https://github.com/stac-utils/pystac/blame/main/CHANGELOG.md#L24 (right after "owner") if you want to sidecar that change in this PR.

[duckontheweb]

I'd like to wait on this release until #704 has been merged since there may be downstream changes to pystac-client to fully address the issue solved by that PR.