OPDATA-3889: FTSE: Use latin1 encoding

[dskloetc]

https://smartcontract-it.atlassian.net/browse/OPDATA-3889

Description

The files we download over SFTP from FTSE are not UTF-8 encoded but rather Latin1 encoded.
This matters because there is a "Ⓡ" (registered trademark) symbol in the Russell index names.
We also have one such file in the fixtures directory but we currently read it with utf-8 encoding.
This means that in the unit tests we need to expect "�" instead of "Ⓡ".
I realized this when trying to add integration tests which failed when using the utf-8 decoded fixtures.

Changes

1. Decode fixture files with latin1 encoding.
2. Replace "�" with "Ⓡ" in tests.

Steps to Test

yarn test packages/sources/ftse-sftp/test

Quality Assurance

• If a new adapter was made, or an existing one was modified so that its environment variables have changed, update the relevant infra-k8s configuration file.
• If a new adapter was made, or an existing one was modified so that its environment variables have changed, update the relevant adapter-secrets configuration file or update the soak testing blacklist.
• If a new adapter was made, or a new endpoint was added, update the test-payload.json file with relevant requests.
• The branch naming follows git flow (feature/x, chore/x, release/x, hotfix/x, fix/x) or is created from Jira.
• This is related to a maximum of one Jira story or GitHub issue.
• Types are safe (avoid TypeScript/TSLint features like any and disable, instead use more specific types).
• All code changes have 100% unit and integration test coverage. If testing is not applicable or too difficult to justify doing, the reasoning should be documented explicitly in the PR.

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