doc: Update application and sample documentation that support nRF9161

[divipillai]

Support of nRF9161 was added to following
applications and samples as part of
#11308:

Asset tracker application
Serial LTE modem application
Memfault sample
Https_client sample
Modem shell sample

This PR updates the documentation of these application and samples.

[NordicBuilder]

You can find the documentation preview for this PR at this link. It will be updated about 10 minutes after the documentation build succeeds.

Note: This comment is automatically posted by the Documentation Publishing GitHub Action.

[divipillai]

@SeppoTakalo @VTPeltoketo @MarkusLassila : Please confirm if updates are correct for Serial LTE modem application documentation. Also, any more updates are required with respect to nRF9161 for the application documentation.

[wiba-nordic]

Prompted by #12173, but Asset Tracker and Serial LTE Modem should also change the corresponding headers in known_issues.rst and release-notes-changelog.rst to match the new page titles. Both can also add a new bullet as the first on on their list:
* Renamed [old name] to [new name].

[divipillai]

Prompted by #12173, but Asset Tracker and Serial LTE Modem should also change the corresponding headers in known_issues.rst and release-notes-changelog.rst to match the new page titles. Both can also add a new bullet as the first on on their list: * Renamed [old name] to [new name].

@wiba-nordic : I have made changes to the change log and Known Issue pages. Since the rename is only at the documentation level and not an overall application rename, the * Renamed [old name] to [new name]. is not added to the pages. 

I have added a changelog entry about nRF9161 support to these applications. Please note that since all the cellular samples will have nRF9161 support, a changelog entry for cellular samples will be added in the PR: #12062 .