add docs for the teltonika integration

[karlbeecken]

Proposed change

This PR is to add the documentation for the new Teltonika integration. Core and Brand PR are linked below.

Type of change

• Spelling, grammar or other readability improvements (current branch).
• Adjusted missing or incorrect information in the current documentation (current branch).
• Added documentation for a new integration I'm adding to Home Assistant (next branch).
  • I've opened up a PR to add logos and icons in Brands repository.
• Added documentation for a new feature I'm adding to Home Assistant (next branch).
• Removed stale or deprecated documentation.

Additional information

• Link to parent pull request in the codebase: add teltonika integration core#157539
• Link to parent pull request in the Brands repository: add Teltonika logos and icons brands#7954
• This PR fixes or closes issue: fixes #

Checklist

• This PR uses the correct branch, based on one of the following:
  • I made a change to the existing documentation and used the current branch.
  • I made a change that is related to an upcoming version of Home Assistant and used the next branch.
• The documentation follows the Home Assistant documentation standards.

[home-assistant]

It seems that this PR is targeted against an incorrect branch. Documentation updates which apply to our current stable release should target the current branch. Please change the target branch of this PR to current and rebase if needed. If this is documentation for a new feature, please add a link to that PR in your description.

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[karlbeecken]

It seems that this PR is targeted against an incorrect branch. Documentation updates which apply to our current stable release should target the current branch. Please change the target branch of this PR to current and rebase if needed. If this is documentation for a new feature, please add a link to that PR in your description.

I linked the Core PR in the description, please remove the needs-rebase label, the next target branch should be correct.

[Copilot]

Pull request overview

This PR adds comprehensive documentation for a new Teltonika integration that enables Home Assistant users to monitor Teltonika Networks routers. The integration focuses on cellular signal monitoring and provides real-time data about modem status and network connectivity.

Key changes:

• Documents the Teltonika integration setup and configuration process
• Lists supported devices (RUT, RUTX, and TRB series routers)
• Describes available sensors for cellular signal monitoring (RSSI, RSRP, RSRQ, SINR, temperature, operator, connection type)