Improve privacy messaging before requesting addition of repository

Created by: rrhyne

Sourcegraph version:3.16 Platform information:MacOS, docker installed, latest chrome.'

Steps to reproduce:

Begin the process of adding a cost host at /site-admin/external-services/new.

Note there is no message to users about how Sourcegraph protects a user's repositories.

Expected behavior:

Users are properly informed of the actions the software will take on their repositories.

Actual behavior:

New users to the platform do not yet trust Sourcegraph with their data, therefore, some users are reluctant to add a code host to their configuration.

Potential solution

Inform the user what the software will do with the access provided. Suggested copy:

How this install accesses your code host: • Clones the repositories you specify to create a local cache • Periodically pulls cloned repositories to ensure search results are current • Collects usage metrics such as number of users, user activity and number of searched repositories • We collect this data to ensure usage does not exceed free software requirements

This installation will not: • Send your code, queries, or other personal data to any online service. Your code and information are private.

The message should be dismiss-able.

See the screenshot: