[DRAFT] Support loading PEM files

[justsmth]

Issues:

Resolves #ISSUE-NUMBER1
Addresses #ISSUE-NUMBER2

Description of changes:

Describe current behavior and how your code changes that behavior. If there are no issues this pr is resolving, explain why this change is necessary.

Call-outs:

Point out areas that need special attention or support during the review process. Discuss architecture or design changes.

Testing:

How is this change tested (unit tests, fuzz tests, etc.)? Are there any testing steps to be verified by the reviewer?

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license and the ISC license.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 75.00000% with 20 lines in your changes missing coverage. Please review.
✅ Project coverage is 92.20%. Comparing base (c358484) to head (ff720b9).
⚠️ Report is 241 commits behind head on main.

Files with missing lines	Patch %	Lines
aws-lc-rs/src/evp_pkey.rs	44.11%	19 Missing ⚠️
aws-lc-rs/src/rsa/key.rs	75.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #860      +/-   ##
==========================================
- Coverage   95.80%   92.20%   -3.60%     
==========================================
  Files          61       71      +10     
  Lines        8143     9357    +1214     
  Branches        0     9357    +9357     
==========================================
+ Hits         7801     8628     +827     
- Misses        342      448     +106     
- Partials        0      281     +281     

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