Feature request - Correct cleanup command to store and use migration project id from metadata db

[darshan-sj]

Support for separate migration project id and spanner project id was added in this PR

In the above PR, for cleanup, migration project id is directly taken from gcloud config. The proper implementation would be to store the migration project id in the metadata DB while initiating the migration. and then use the stored migration project id to cleanup the migration resources.

Pending tasks:

• metadata db schema changes to store migration project id
• Changes to store migration project id.
• Changes in cleanup command to use the migration project id from the metadata db.