[WIP]Changing naming from tier to SSP

[vineela1999]

What type of PR is this?

Uncomment only one /kind <> line, hit enter to put that in a new line, and remove leading whitespace from that line:

/kind new feature
/kind bug fix
/kind cleanup
/kind revert change
/kind design
/kind documentation

kind enhancement

What this PR does / why we need it:
This PR is needed to use the terminology SSP instead tier because tier in our multi-cloud refers to storage class levels
This PR changes all the tiering API
Which issue(s) this PR fixes:

Fixes #

Test Report Added?:

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/kind TESTED
/kind NOT-TESTED

Test Report:

Special notes for your reviewer:

[codecov]

Codecov Report

Merging #1307 (18f9ab6) into master (bb06780) will not change coverage.
The diff coverage is 86.48%.

@@           Coverage Diff           @@
##           master    #1307   +/-   ##
=======================================
  Coverage   48.12%   48.12%           
=======================================
  Files          10       10           
  Lines        1571     1571           
=======================================
  Hits          756      756           
  Misses        756      756           
  Partials       59       59           

Impacted Files	Coverage Δ
backend/pkg/service/service.go	79.76% <86.48%> (ø)