Add Tiers improvements for Bucket Lifecycle management

[cesnietor]

There are places where we only need to list the Tiers' names including: Add Lifecycle Rule, Bulk add LifecycleRule and EditLifeCycleRule for Buckets. However we were using the listTiers API which does two extra requests including; getting tier stats and verification (verifies endpoint can perform needed requests).
Since we only need the names I've added a new api which does only that.
There were also some issues in the tests for tiersList which I also addressed here.
This makes the requests much faster to give a better user experience.

Changes:

• Add new API: admin/tiers/names
• Include tests for getTiersName
• Fix tests for getTiers (were were not checking the result from the response)
• Use of map to avoid iterating on the tierStats response on every tier for getTiers

Test Steps:

With an authenticated users and TIERS configured do a GET on:

http://localhost:9090/api/v1/tiers/names

Response comes as:

{
    "items": [
        "PLAY-TIER",
        "SOME-TIER-CONFIG"
    ]
}

Test Steps with UI:

For Bulk Lifecycle:

• Add Tiers
• Create two buckets with Versioning enabled
• Go to Administrator/Buckets and click on Select Multiple buckets Icon
• Select multiple buckets
• Click on Set Lifecycle button
• Click on Transition (the list of tiers should appear)

For Add Bucket Lifecycle:

• Go to Administrator/Buckets and click on one
• Click on Lifecycle
• Click on Add Lifecycle rule
• Click on Transition (the list of tiers should appear)

For Add Bucket Lifecycle:

• Go to Administrator/Buckets and click on one with lifecycle rules
• Click on one rule
• List of tiers should appear

Screenshots of it working:

Edit:

Add:

Bulk:

[prakashsvmx]

Verified. LGTM 👍

hope , fix for ci failure is part of #3381

[bexsoft]

LGTM