Add Codable support for Context and unsafe add functionality

[Supereg]

Add Codable support for Context and unsafe add functionality

♻️ Current situation & Problem

Currently Context is not modifiable and Context is not encodable.

E.g. ApodiniMigrator has the use case to store gRPC related information within the Context of a TypeInformation. This requires:

• Ability to modify the Context of a TypeInformation instance after it has been created as otherwise the only source for Context information are Metadata declaration blocks on Content types
• Ability to encode and decode (if explicitly declared) ContextKeys

💡 Proposed solution

This PR adds a unsafeAdd method which can be used if appropriate. Further Context is made Codable, supporting lossy encoding and decoding of ContextKeys which declare conformance to CodableContextKey.

⚙️ Release Notes

• Added new CodableContextKey for ContextKeys which Value support Codable.

➕ Additional Information

Related PRs

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Testing

According tests were added.

Reviewer Nudging

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Code of Conduct & Contributing Guidelines

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• I agree to follow the Code of Conduct and Contributing Guidelines.

[codecov]

Codecov Report

Merging #3 (03cdc0a) into develop (2f3f03f) will decrease coverage by 1.44%.
The diff coverage is 87.00%.

@@             Coverage Diff             @@
##           develop       #3      +/-   ##
===========================================
- Coverage    92.16%   90.73%   -1.43%     
===========================================
  Files           22       23       +1     
  Lines          395      485      +90     
===========================================
+ Hits           364      440      +76     
- Misses          31       45      +14     

Impacted Files	Coverage Δ
Sources/ApodiniContext/ContextKey.swift	100.00% <ø> (ø)
Sources/ApodiniContext/CodableContextKey.swift	84.62% <84.62%> (ø)
Sources/ApodiniContext/Context.swift	87.63% <86.75%> (-12.37%)	⬇️
Sources/ApodiniContext/ContextEntry.swift	83.08% <100.00%> (ø)
Sources/ApodiniContext/ContextNode.swift	99.16% <100.00%> (-<0.01%)	⬇️

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