Remove "not used" params in BBS migrations

[synthead]

Bitbucket Server migrations are archive-only and BBS instances are assumed to be unreachable from the internet. Therefore, Octoshift will never reach out to source instances, and a source PAT is not required. Additionally, BBS migration archives are only single archives that we move using the gitArchiveUrl GraphQL field for startMigration mutations. Therefore, we never use metadataArchiveUrl field.

We have updated the public GraphQL interface to make these two parameters optional. Prior to this, we added filler "not used" values for accessToken and metadataArchiveUrl to satisfy the GraphQL request requirements. These ignored "filler" values are not necessary anymore, so this PR removes them! :sparkles:

• [ ] Did you write/update appropriate tests
• [ ] Release notes updated (if appropriate)
• [ ] Appropriate logging output
• [ ] Issue linked
• [ ] Docs updated (or issue created)
• [ ] New package licenses are added to ThirdPartyNotices.txt (if applicable)

[github-actions[bot]]

Unit Test Results

780 tests   778 :heavy_check_mark:  23s :stopwatch:     1 suites      0 :zzz:     1 files        2 :x:

For more details on these failures, see this check.

Results for commit f9a59290.

[github-actions[bot]]

Package	Line Rate	Branch Rate	Complexity	Health
bbs2gh	79%	75%	573	✔
ado2gh	84%	82%	617	✔
gei	83%	79%	652	✔
Octoshift	85%	75%	1168	✔
Summary	84% (6490 / 7765)	77% (1572 / 2042)	3010	✔