Invalid links in markdown files

[jackielii]

Tell us about the documentation you'd like us to add or update.

While going through the handbook, I found broken link. Then made a little script that detects the invalid links.

If applicable, add links to the relevant docs that should be updated

file: airbyte-integrations/connectors/destination-firestore/README.md
Broken link: [the documentation](https://docs.airbyte.io/integrations/destinations/firestore)

file: airbyte-integrations/connectors/source-appsflyer/README.md
Broken link: [documentation](https://docs.airbyte.io/integrations/sources/appsflyer)

file: airbyte-integrations/connectors/source-appsflyer/README.md
Broken link: [the documentation](https://docs.airbyte.io/integrations/sources/appsflyer)

file: airbyte-integrations/connectors/source-mailgun/README.md
Broken link: [documentation](https://docs.airbyte.io/integrations/sources/mailgun)

file: airbyte-integrations/connectors/source-mailgun/README.md
Broken link: [the documentation](https://docs.airbyte.io/integrations/sources/mailgun)

file: airbyte-integrations/connectors/source-pardot/README.md
Broken link: [the documentation](https://docs.airbyte.io/integrations/sources/pardot)

file: airbyte-integrations/connectors/source-pardot/README.md
Broken link: [documentation](https://docs.airbyte.io/integrations/sources/pardot)

file: docs/career-and-open-positions/senior-software-engineer.md
Broken link: [roadmap](https://docs.airbyte.io/roadmap)

file: docs/contributing-to-airbyte/updating-documentation.md
Broken link: [internal guide for deployment lives here](https://github.com/airbytehq/runbooks/blob/master/deploying_and_reverting_docs.md)

file: docs/contributing-to-airbyte/updating-documentation.md
Broken link: [dedicated repo hosting the Github pages](https://github.com/airbytehq/airbytehq.github.io)

[Rajakavitha1]

file: airbyte-integrations/connectors/destination-firestore/README.md
Broken link: [the documentation](https://docs.airbyte.io/integrations/destinations/firestore)]
Related .md file is not located at https://github.com/airbytehq/airbyte/tree/master/docs/integrations/destinations
file: airbyte-integrations/connectors/source-appsflyer/README.md
Broken link: [documentation](https://docs.airbyte.io/integrations/sources/appsflyer)]
Related .md file is not located at https://github.com/airbytehq/airbyte/tree/master/docs/integrations/sources
file: airbyte-integrations/connectors/source-appsflyer/README.md
Broken link: [the documentation](https://docs.airbyte.io/integrations/sources/appsflyer)]
[Redundant]
Related .md file is not located at https://github.com/airbytehq/airbyte/tree/master/docs/integrations/sources
file: airbyte-integrations/connectors/source-mailgun/README.md
Broken link: [documentation](https://docs.airbyte.io/integrations/sources/mailgun)]
Related .md file is not located at https://github.com/airbytehq/airbyte/tree/master/docs/integrations/sources
file: airbyte-integrations/connectors/source-mailgun/README.md
Broken link: [the documentation](https://docs.airbyte.io/integrations/sources/mailgun)]
[Redundant]
file: airbyte-integrations/connectors/source-pardot/README.md
Broken link: [the documentation](https://docs.airbyte.io/integrations/sources/pardot)]
Related .md file is not located at https://github.com/airbytehq/airbyte/tree/master/docs/integrations/sources
file: airbyte-integrations/connectors/source-pardot/README.md
Broken link: [documentation](https://docs.airbyte.io/integrations/sources/pardot)]
[Redundant]

Related issues:

• Google Firestore missing documentation #12808
• https://github.com/airbytehq/airbyte-internal-issues/issues/614