feat: lake: Reservoir-related configuration for packages

[tydeu]

Adds additional fields to the package configuration which will be used by Reservoir:

• version: The version of the package. Follows Lean's model of <major>.<minor>.<patch>[-<specialDescr>].
• versionTags: A pattern matching the set of Git tags Reservoir should consider package version revisions.
• description: A short description for the package. Takes precedence over the GitHub's description.
• keywords: An array of package keywords that will be used to group packages into categories on Reservoir. Takes precedence over labels on the repository.
• homepage: A URL to a website for the package. Takes precedence over GitHub's homepage.
• license: An SPFX license identifier for the package's license (not verified to be well-formed).
• licenseFiles: An array of (relative) files the contain license information (e.g., #["LICENSE", "NOTICE"] for Apache 2.0).
• readmeFile: Relative path to the package's readme (enables non-standard README locations).
• reservoir: Reservoir will use this setting to determine whether to include packages in its index.

Also adds two new CLI commands:

• lake reservoir-config: Used by Reservoir to extract a package's configuration.
• lake check-build: Determines whether the package has any default build targets configured.

The Reservoir configuration also makes uses of the exiting name and platformIndependent fields.

[leanprover-community-mathlib4-bot]

Mathlib CI status (docs):

• ✅ Mathlib branch lean-pr-testing-4770 has successfully built against this PR. (2024-07-17 04:16:31) View Log
• ✅ Mathlib branch lean-pr-testing-4770 has successfully built against this PR. (2024-07-17 17:19:21) View Log
• ✅ Mathlib branch lean-pr-testing-4770 has successfully built against this PR. (2024-07-18 00:47:34) View Log
• ✅ Mathlib branch lean-pr-testing-4770 has successfully built against this PR. (2024-07-19 17:23:37) View Log
• ✅ Mathlib branch lean-pr-testing-4770 has successfully built against this PR. (2024-08-30 06:35:25) View Log
• ✅ Mathlib branch lean-pr-testing-4770 has successfully built against this PR. (2024-08-31 00:02:42) View Log
• ✅ Mathlib branch lean-pr-testing-4770 has successfully built against this PR. (2024-08-31 07:26:41) View Log
• ✅ Mathlib branch lean-pr-testing-4770 has successfully built against this PR. (2024-09-02 16:59:28) View Log