Add project creation to Elasticsearch Getting Started

[lcawl]

Relates to #1480

This PR:

• creates a drop-down in https://www.elastic.co/docs/solutions/search/get-started to contain project creation tips, similar to https://www.elastic.co/docs/solutions/observability/get-started. To avoid getting out of sync with https://www.elastic.co/docs/deploy-manage/deploy/elastic-cloud/create-serverless-project, the shared content is moved to a snippet.
• adds Information about the authority required to create projects (derived from https://www.elastic.co/docs/solutions/observability/get-started) to the snippet
• re-uses the same snippet in the "create a project" step in one of the quickstarts
• adds a link from the search ingestion page to the "find your connection details" page
• updates links from the serverless deployment pages to target https://www.elastic.co/docs/solutions/search/get-started

[github-actions]

🔍 Preview links for changed docs

• deploy-manage/deploy/elastic-cloud/create-serverless-project.md
• deploy-manage/deploy/elastic-cloud/serverless.md
• solutions/search/get-started.md
• solutions/search/get-started/keyword-search-python.md
• solutions/search/ingest-for-search.md

[shainaraskas]

changes to deploy-manage area good to go

[szabosteve]

LGTM!