add FromEnvVar support for providers

[ppyt-pl]

Description of your changes

Fixes https://github.ibm.com/IBMPrivateCloud/roadmap/issues/50545

I have:

• Read and followed Crossplane's contribution process.
• Run make reviewable to ensure this PR is ready for review.
• Added backport release-x.y labels to auto-backport this PR if necessary.

if the new changes require, also:

• Extended the tests in BedrockShim repo or created an issue for it.
  These tests should cover for example checking new expected resources or their content.

How has this code been tested

[ibm-ci-bot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

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[codecov]

Codecov Report

Base: 67.09% // Head: 67.15% // Increases project coverage by +0.05% 🎉

Coverage data is based on head (32473cf) compared to base (d6f0124).
Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #65      +/-   ##
==========================================
+ Coverage   67.09%   67.15%   +0.05%     
==========================================
  Files          67       67              
  Lines        4382     4390       +8     
==========================================
+ Hits         2940     2948       +8     
  Misses       1304     1304              
  Partials      138      138              

Flag	Coverage Δ
unittests	67.15% <100.00%> (+0.05%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
internal/controller/pkg/manager/reconciler.go	55.81% <100.00%> (+2.15%)	⬆️

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