[cache] Layer caching during SBOM generation

[prabhu]

What if cdxgen creates a cache directory to cache the output from the external commands and APIs and reuse it upon subsequent invocation (with the --enable-cache argument or default in CI environments)?

• Unique key generation could be based on the hashes of the input files used (which are available as a property)
• Some caching can be performed as a postgen step
• In CI environments, users could load the cache in advance by utilizing the in-built caching step
• We can offer commands to clear the cache

[prabhu]

https://github.com/sindresorhus/got/blob/main/documentation/cache.md#cache