Missena: Update parameters and add versioning support

[ysfbsf]

Description

This PR updates the Missena adapter with several improvements to enhance clarity and functionality.

Changes

• Renamed parameter: Changed TestMode to Sample for better clarity and understanding
• Added APIKey support: Added APIKey field to UserParams struct to properly pass API keys in requests
• Enhanced version string: Improved version string formatting to include "prebid-server@" prefix for better identification
• Updated tests: Modified all test files to reflect the new parameter structure and version format

Type of change

• [ ] Bug fix (non-breaking change which fixes an issue)
• [x] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [ ] This change requires a documentation update

Testing

All existing tests have been updated and are passing:

go test ./adapters/missena/...

Checklist

• [x] I have performed a self-review of my own code
• [x] I have commented my code, particularly in hard-to-understand areas
• [x] I have made corresponding changes to the documentation
• [x] My changes generate no new warnings
• [x] I have added tests that prove my fix is effective or that my feature works
• [x] New and existing unit tests pass locally with my changes

[github-actions[bot]]

Code coverage summary

Note:

• Prebid team doesn't anticipate tests covering code paths that might result in marshal and unmarshal errors
• Coverage summary encompasses all commits leading up to the latest one, 7a9e08816204bd86a10d2f2a9c56318a257d9981

missena

Refer here for heat map coverage report

github.com/prebid/prebid-server/v3/adapters/missena/missena.go:60:	Builder			80.0%
github.com/prebid/prebid-server/v3/adapters/missena/missena.go:71:	getVersionString	66.7%
github.com/prebid/prebid-server/v3/adapters/missena/missena.go:78:	getCurrency		88.9%
github.com/prebid/prebid-server/v3/adapters/missena/missena.go:94:	getEndPoint		100.0%
github.com/prebid/prebid-server/v3/adapters/missena/missena.go:101:	makeRequest		80.6%
github.com/prebid/prebid-server/v3/adapters/missena/missena.go:179:	MakeRequests		89.5%
github.com/prebid/prebid-server/v3/adapters/missena/missena.go:215:	readGDPR		100.0%
github.com/prebid/prebid-server/v3/adapters/missena/missena.go:235:	MakeBids		94.1%
total:									(statements)		87.4%