[DB-15395] Fix the IOPs calculation logic from considering seq_tup_read as reads to using number of scans(sequential and index)

[sanyamsinghal]

Describe the changes in this pull request

The change is for the bug identified where assess-migration command was reporting a very large cluster(number of nodes) even for a substantially small clusters.

Fixed the logic to make use of seq_scan and idx_scan of pg_stat_user_tables
Experiments results captured in sheet - https://docs.google.com/spreadsheets/d/177NIv6UPsL_TmQ2J9nLTPiEU2p_nYHHnDZvRMefcnbk/edit?usp=sharing

For example: A simple case where seq scans are happening

CREATE TABLE test_data (
    id SERIAL PRIMARY KEY,
    value TEXT
);

INSERT INTO test_data (value)
SELECT md5(random()::text) FROM generate_series(1, 100000);

— reads (seq scans)
DO $$ 
DECLARE i INT;
BEGIN
    FOR i IN 1..100 LOOP
        PERFORM COUNT(*) FROM test_data;
    END LOOP;
END $$;

Here earlier voyager was recommending - 34Nodes of 8vcpu instance types (screenshot 1)
Now recommending - 3 node 4vcpu instance types (screenshot 2)

screenshot 1:

screenshot 2:

Describe if there are any user-facing changes

No. Only the actual recommendations would change based on the new logic(statistics changed)

How was this pull request tested?

Does your PR have changes that can cause upgrade issues?

Component	Breaking changes?
MetaDB	Yes/No
Name registry json	Yes/No
Data File Descriptor Json	Yes/No
Export Snapshot Status Json	Yes/No
Import Data State	Yes/No
Export Status Json	Yes/No
Data .sql files of tables	Yes/No
Export and import data queue	Yes/No
Schema Dump	Yes/No
AssessmentDB	Maybe (changed the struct of TableIndexStats table)
Sizing DB	Yes/No
Migration Assessment Report Json	Maybe(Report will be changed wrt TableIndexStats)
Callhome Json	Yes/No
YugabyteD Tables	Yes/No
TargetDB Metadata Tables	Yes/No

[sanyamsinghal]

https://jenkins.dev.yugabyte.com/job/users/job/yb-voyager-testing/job/yb-voyager-testing-pipeline/4850/