Port 1.x influxd backup and restore commands

[stuartcarnie]

What

Users will require backup and restore capabilities. Port the TSM backup and restore commands from 1.x and integrate with 2.x.

• influx backup
• influx restore

2.0 Backup (prior to TSM 1.x transition)

The 2.0 backup / restore command can be summarized as the following:

• Online backup and offline restore
• Backup all meta data
• Backup all buckets

This approach is limited and largely governed by the storage architecture, best described as a single database and single shard. All buckets were co-mingled in a single set of TSM files.

2.0 Backup

The OSS 1.8 backup system is considerably more powerful and flexible per the documentation.

With the transition to the TSM 1.x storage engine, the on-disk structure lends itself to the same backup / restore features. This layout is discussed in #19114, however, it is included below for reference:

data/
  bucket-a/
    autogen/
      <shardid-1>/
        *.tsm
      <shardid-2>/
        *.tsm
  bucket-b/
    autogen/
      <shardid-1>/
        *.tsm

In summary, each bucket is now represented as a single database and retention policy and is made up of one or more shards.

Given that, many of the features of 1.8 can be ported, including

• Online backup and restore
• Backup of individual buckets (database / retention policy in 1.x parlance)
• Backup of individual shards (single shard from a single bucket)

[stephanie-engel]

Once this fix is implemented, the litmus backup and restore tests will need to be un-skipped.

[benbjohnson]

Update: Backup/restore PR is up: #19864

[benbjohnson]

Completed & merged into master.