fix: prefix for compact numbers

[gulfaraz]

Describe your changes

This PR includes follow up changes on design feedback for https://github.com/rodekruis/Anticipatory-Action/issues/644

1. Show whole numbers for percentage values.
2. Update functions so that,
   • 0 becomes 0
   • 2 becomes < 10
   • 12 becomes < 20
   • 20 becomes 20
   • 56 becomes 60
   • 297 becomes 300
   • 462 becomes 460
   • 1000 becomes 1K
   • 4200 becomes 4.2K
   • 225305 becomes 230K
   • 79136946 becomes 79M
   • negative numbers become 0

Checklist before requesting a review

• I have performed a self-review of my code
• I have added tests wherever relevant
• I have made sure that all automated checks pass before requesting a review

Notes for the reviewer

1. For testing, I set value = 12 at the start of the transform function.

[gulfaraz]

> test:api:all
> node --expose-gc node_modules/.bin/jest --config=jest.api.config.js --runInBand --detectOpenHandles --logHeapUsage

ts-jest[versions] (WARN) Version 4.9.5 of typescript installed has not been tested with ts-jest. If you're experiencing issues, consider using a supported version (>=2.7.0 <4.0.0). Please do not report issues in ts-jest if you are using unsupported versions.
 PASS  test/email/drought/email-uga-drought.test.ts (17.266s, 214 MB heap size)
  Should send an email for uga drought
    ✓ triggered in january (7401ms)
    ✓ non triggered any month (8072ms)

 PASS  test/email/floods/email-uga-floods.test.ts (37.762s, 215 MB heap size)
  Should send an email for uga floods
    ✓ default (9045ms)
    ✓ warning (9022ms)
    ✓ warning-to-trigger (10493ms)
    ✓ no-trigger (8876ms)

 PASS  test/email/floods/email-ssd-floods.test.ts (16.398s, 225 MB heap size)
  Should send an email for ssd floods
    ✓ default (9627ms)
    ✓ no-trigger (6401ms)

 PASS  test/email/flash-flood/email-mwi-flash-flood.test.ts (32.421s, 226 MB heap size)
  Should send an email for mwi flash flood
    ✓ default (8794ms)
    ✓ no-trigger (23358ms)

 PASS  test/email/malaria/email-eth-malaria.test.ts (16.602s, 217 MB heap size)
  Should send an email for eth malaria
    ✓ default (7470ms)
    ✓ no-trigger (8864ms)

 PASS  test/email/dengue/email-phl-dengue.test.ts (16.106s, 217 MB heap size)
  Should send an email for phl dengue
    ✓ default (8223ms)
    ✓ no-trigger (7603ms)

 PASS  test/email/typhoon/email-phl-typhoon.test.ts (11.445s, 234 MB heap size)
  Should send an email for phl typhoon
    ✓ default (11189ms)

Test Suites: 7 passed, 7 total
Tests:       15 passed, 15 total
Snapshots:   0 total
Time:        148.777s
Ran all test suites.