Add methods to directly add Reference Values and Endorsed Values

[Priyanshuthapliyal2005]

Files Added/Modified:

comid/comid.go
comid/comid_test.go
comid/digests.go
comid/hashalg.go
comid/hashalg_test.go
comid/valuetriple.go

Issue Addressed:

This pull request addresses #136 which highlights the difficulty in introducing Extensions for Reference Value Measurements using the current Extensions Interface.

###** Solution:**
New methods have been introduced to the CoMID struct to facilitate the addition of Reference Values without requiring the creation of instances for Measurement and ValueTriples. These methods include:

AddSimpleReferenceValue
AddDigestReferenceValue
AddRawReferenceValue
AddReferenceValueDirect
AddEndorsedValueDirect
These enhancements streamline the process, making it easier to add Reference Values and ensuring better usability of the Extensions Interface.

Before:

Users had to manually create instances for Measurement and ValueTriples to add Reference Values, which was cumbersome and error-prone.

Example:

measurement := &Measurement{ /* initialize measurement */ }
valueTriple := ValueTriple{
Environment: env,
Measurements: *NewMeasurements().Add(measurement),
}
comid.Triples.ReferenceValues.Add(valueTriple)

### After:
With the new methods, users can directly add Reference Values without creating these instances, significantly simplifying the process and reducing the likelihood of errors.

Example:

err := comid.AddSimpleReferenceValue(env, measurement)
if err != nil {
log.Fatalf("failed to add reference value: %v", err)
}