Make where we work with BOSH Release tarballs explicit

[crhntr]

TL;DR

• component.Spec and cargo.ComponentSpec -> cargo.BOSHReleaseTarballSpecification
• component.Lock and cargo.ComponentLock -> cargo.BOSHReleaseTarballLock
• cargo.ReleaseSourceTypeBOSHIO -> cargo.BOSHReleaseTarballSourceTypeBOSHIO
• cargo.ReleaseSourceTypeS3 -> cargo.BOSHReleaseTarballSourceTypeS3
• cargo.ReleaseSourceTypeGithub -> cargo.BOSHReleaseTarballSourceTypeGithub
• cargo.ReleaseSourceTypeArtifactory -> cargo.BOSHReleaseTarballSourceTypeArtifactory
• a few other function and method names were changed in a similar way to align with the above rename operations.

Discussion

This refactor is intended to make it easier to think about and code around the BOSH releases tarballs we package.

• In 96032c8, I merge component.Lock and cargo.ComponentLock. They have literally been the same thing for a while; this commit removes the indirection.
  • component.Local and component.Exported no longer embed the cargo.ComponentLock but have it as a non-embedded field. This makes refactors easier and makes it clear that those types should not inherit methods from the Lock. For the most part, this change is reversible in a non-breaking way.
• In a67fdfd, I rename "Component{Lock,Spec} to BOSHRelease{Lock,Spec}. We may still want to refer to BOSH Releases as tile components in speech and docs but the code reads better when it is less ambiguous about what is is operating on.
• In f0f1656, I add the Tarball part to the BOSHRelease names.
• In 7977710, I renamed other public identifiers and methods to stay consistent with the Tarball Lock and Spec types.

[cf-gitbot]

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[crhntr]

Here is some "prior art". PR #405 is bigger because it merges and renames; the prior art commit does not merge the types it just renames cargo type.

[dtimm]

Excellent refactor. LGTM.