Update generic thermostat strings for clarity and accuracy

[maxshcherbina]

Proposed change

Per #130030, I removed "helper" from the title for consistency.
Per #128341, Updated the grammar on target_sensor.
On min_cycle_duration, I changed the keep_alive option to make it more clear that it is a YAML only option. This addresses #128732.

I will work on #128109 next, but as its a larger change, I didnt want to include it in this PR.

Type of change

• Dependency upgrade
• Bugfix (non-breaking change which fixes an issue)
• New integration (thank you!)
• New feature (which adds functionality to an existing integration)
• Deprecation (breaking change to happen in the future)
• Breaking change (fix/feature causing existing functionality to break)
• Code quality improvements to existing code or addition of tests

Additional information

• This PR fixes or closes issue:
• fixes Generic Thermostat: Several strings to clean up #130030
• fixes Generic Thermostat: Unclear reference to "Keep alive" option, crammed entry field #128732
• fixes Typo in component::generic_thermostat::config::step::user::data_description::target_sensor #128341
• This PR is related to issue:
• Generic Thermostat: Several strings to clean up #130030
• Generic Thermostat: Unclear reference to "Keep alive" option, crammed entry field #128732
• Typo in component::generic_thermostat::config::step::user::data_description::target_sensor #128341
• Small inconsistencies in Create/Add dialogs for different Helper types #128109
• Link to documentation pull request: https://www.home-assistant.io/integrations/generic_thermostat/

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[joostlek]

If you prefix all the issues that should be closed with merging this, make sure you note them as fixes #123

[maxshcherbina]

If you prefix all the issues that should be closed with merging this, make sure you note them as fixes #123

What is the appropriate terminology for if it fixes only one of the things listed in the issue?
In any case, fixed the prefixes!

[home-assistant]

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[frenck]

Thanks, @maxshcherbina 👍

../Frenck