feat: add SRVI and SRWI indices to Sentinel-2 collection

[c-chrysostomou]

Description

This Pull Request introduces two new subfolders to the sentinel-2/ collection containing scripts and documentation for two optimized spectral indices discovered via symbolic regression:

1. SRVI (Symbolic Regression Vegetation Index): A 4-band index (B03, B04, B08, B11) designed for improved vegetation mapping and high-biomass sensitivity.
2. SRWI (Symbolic Regression Water Index): A 4-band index (B02, B03, B08, B11) optimized for surface water mapping with reduced false positives from terrain shadows and urban structures.

Changes Included

• Added sentinel-2/srvi/script.js & sentinel-2/srvi/README.md
• Added sentinel-2/srwi/script.js & sentinel-2/srwi/README.md
• Configured YAML front-matter with standard metadata, links to the raw script locations, and example coordinates.

Reference Publication

• Paper: Optimized spectral indices for global vegetation and water mapping using Sentinel-2
• Journal: Nature Scientific Reports (2026)
• DOI: https://doi.org/10.1038/s41598-025-34720-x
• Contributor: https://github.com/c-chrysostomou

[beltran-sinergise]

Please add a reference to your script in the corresponding top-level markdown file (sentinel-2/sentinel-2.md), e.g., under Remote sensing indices:

- [SRVI](/sentinel-2/srvi) - symbolic regression vegetation index

For more details, see

custom-scripts/README.md

Lines 33 to 34 in 331b300

	- Add an entry pointing to your script to the top level markdown file (i.e. if adding a script for Sentinel 2 add the link to `sentinel-2.md` in the folder `sentinel-2`).
	_A link and a short description will do._

[beltran-sinergise]

Please add a reference to your script in the corresponding top-level markdown file (sentinel-2/sentinel-2.md), e.g., under Remote sensing indices:

- [SRWI](/sentinel-2/srwi) - symbolic regression water index

For more details, see

custom-scripts/README.md

Lines 33 to 34 in 331b300

	- Add an entry pointing to your script to the top level markdown file (i.e. if adding a script for Sentinel 2 add the link to `sentinel-2.md` in the folder `sentinel-2`).
	_A link and a short description will do._

[beltran-sinergise]

Please set up the evalscripturl parameter the recommended way, i.e., pointing to this repository:

    evalscripturl: https://custom-scripts.sentinel-hub.com/custom-scripts/sentinel-2/srvi/script.js

For more details, see contribute/example/index.md

[beltran-sinergise]

Please set up the evalscripturl parameter the recommended way, i.e., pointing to this repository:

    evalscripturl: https://custom-scripts.sentinel-hub.com/custom-scripts/sentinel-2/srwi/script.js

For more details, see contribute/example/index.md