* logging: added Logger.Debugw(message, key1, value1, ..., keyN, valueN)
This is based on ZAP and allows structural logs to be emitted.
* cli: added --json-log-console and --json-log-file flags
* logging: updated storage logging wrapper to use structural logging
* pr feedback
* testing: KOPIA_TEST_LOG_OUTPUT logs subcommand outputs
* cli: additional flags for 'blob list'
* Makefile: run all tests against epoch-based index manager
* epoch: added support for deletion watermark, which keeps track of latest maintenance which dropped index entries
* content: added deletion watermark to content manager
* maintenance: improved maintenance without safety to force rewrites
* maintenance: skip quick maintenance when epoch manager is enabled
* maintenance: do not enable quick maintenance when epoch manager is used
* testing: skip TestIndexOptimize when running against epoch manager-backed index strutures
* epoch: misc fixes and logging
* blob: misc helpers
* cli: removed useless 'repository upgrade', replaced by 'repository set-parameters'
* content: implemented indexBlobManagerV1 which uses epoch manager
* cli: commands to manipulate repository epoch parameters
* cli: commands to examine epoch-based indexes
* content: added test suite that uses epoch-based index manager
* content: fixed a ton of test data races caused by sharing blobtesting.DataMap
* cli: additional tests and validation for 'repository set-params'
* testing: replaced the use of suite with our own, since suite is not parallelizable
* refactor: extracted complete blob set functions to separate package
* completeset: added more functions
Also treat malformed blob IDs as their own sets for backwards compat.
