[vtadmin-api] Update GetTablet to use alias instead of hostname

[doeg]

Signed-off-by: Sara Bee 855595+doeg@users.noreply.github.com

Description

Since tablet hostnames alone aren't guaranteed to be unique even in the same cluster (as with the local example), this updates the /api/tablet/{tablet} and /experimental/tablet/{tablet}/debug/vars endpoints to use tablet alias as an identifier instead.

No changes required to vtadmin-web for this; it doesn't use these endpoints yet.

An example:

$ curl "http://localhost:14200/api/tablet/zone1-102" | jq .
{
  "result": {
    "cluster": {
      "id": "id1",
      "name": "cluster1"
    },
    "tablet": {
      "alias": {
        "cell": "zone1",
        "uid": 102
      },
      "hostname": "a4c88ebf1fe6",
      "keyspace": "commerce",
      "shard": "0",
      "type": 3
    },
    "state": 1
  },
  "ok": true
}

...and an example of an error when an invalid alias is given (which the existing tests already cover):

$ curl "http://localhost:14200/api/tablet/does-not-exist" | jq .
{
  "error": {
    "message": "failed to parse tablet_alias does-not-exist: invalid tablet alias: 'does-not-exist', expecting format: '<cell>-<uid>'",
    "code": "unknown"
  },
  "ok": false
}

Related Issue(s)

N/A

Checklist

• Tests were added or are not required
• Documentation was added or is not required

Deployment Notes

N/A

[rafael]

Makes sense to me. LGTM