(MINOR) Add sign feature for signing manifests without file I/O

[gpeacock]

Changes in this pull request

Add sign feature for signing manifests without file i/o Only supports jpeg in so far Manifest.embed_stream method added

Checklist

• [ ] This PR represents a single feature, fix, or change.
• [ ] All applicable changes have been documented.
• [ ] Any TO DO items (or similar) have been entered as GitHub issues and the link to that issue has been included in a comment.

[codecov-commenter]

Codecov Report

Merging #125 (87fc945) into main (b167bae) will increase coverage by 0.10%. The diff coverage is 88.81%.

@@            Coverage Diff             @@
##             main     #125      +/-   ##
==========================================
+ Coverage   78.26%   78.37%   +0.10%     
==========================================
  Files          67       67              
  Lines       14656    14899     +243     
==========================================
+ Hits        11471    11677     +206     
- Misses       3185     3222      +37     

Impacted Files	Coverage Δ
sdk/src/assertions/exif.rs	78.16% <ø> (ø)
sdk/src/asset_io.rs	50.00% <ø> (ø)
sdk/src/claim.rs	82.98% <ø> (ø)
sdk/src/create_signer.rs	31.03% <ø> (ø)
sdk/src/error.rs	14.28% <ø> (ø)
sdk/src/hashed_uri.rs	76.92% <ø> (ø)
sdk/src/lib.rs	100.00% <ø> (ø)
sdk/src/openssl/ec_signer.rs	85.21% <ø> (-2.29%)	:arrow_down:
sdk/src/openssl/ec_validator.rs	96.42% <ø> (ø)
sdk/src/openssl/ed_signer.rs	70.58% <ø> (-1.02%)	:arrow_down:
... and 23 more

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